Honor CMAKE_<LANG>_FLAGS[_<CONFIG>]_INIT set in toolchain files

Document these variables.

Change our convention for setting these variables from:

    set(CMAKE_C_FLAGS_INIT "...")

to

    string(APPEND CMAKE_C_FLAGS_INIT " ...")

so that any value previously set by a toolchain file will be used.

Automate the conversion with:

    sed -i 's/set *(\(CMAKE_\(C\|CXX\|Fortran\|RC\|ASM\|${[^}]\+}\)_FLAGS\(_[^_]\+\)\?_INIT \+"\)/string(APPEND \1 /' \
      Modules/Compiler/*.cmake Modules/Platform/*.cmake

and follow up with some manual fixes (e.g. to cases that already
meant to append).  Also revert the automated changes to contexts
that are not protected from running multiple times.

Help/manual/cmake-variables.7.rst

@@ -344,10 +344,15 @@ Variables for Languages
    /variable/CMAKE_LANG_CREATE_SHARED_MODULE
    /variable/CMAKE_LANG_CREATE_STATIC_LIBRARY
    /variable/CMAKE_LANG_FLAGS_DEBUG
+   /variable/CMAKE_LANG_FLAGS_DEBUG_INIT
    /variable/CMAKE_LANG_FLAGS_MINSIZEREL
+   /variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT
    /variable/CMAKE_LANG_FLAGS_RELEASE
+   /variable/CMAKE_LANG_FLAGS_RELEASE_INIT
    /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO
+   /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT
    /variable/CMAKE_LANG_FLAGS
+   /variable/CMAKE_LANG_FLAGS_INIT
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_DEBUG
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_MINSIZEREL
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_RELEASE

Help/release/dev/toolchain-flag-init.rst

@@ -0,0 +1,7 @@
+toolchain-flag-init
+-------------------
+
+* :variable:`Toolchain files <CMAKE_TOOLCHAIN_FILE>` may now set a
+  :variable:`CMAKE_<LANG>_FLAGS_INIT` variable to initialize the
+  :variable:`CMAKE_<LANG>_FLAGS` cache entry the first time a language is
+  enabled in a build tree.

Help/variable/CMAKE_LANG_FLAGS_DEBUG_INIT.rst

@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_DEBUG_INIT
+-----------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_DEBUG` cache
+entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_INIT.rst

@@ -0,0 +1,15 @@
+CMAKE_<LANG>_FLAGS_INIT
+-----------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS` cache entry
+the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also the configuration-specific variables:
+
+* :variable:`CMAKE_<LANG>_FLAGS_DEBUG_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELEASE_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT`

Help/variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT.rst

@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT
+----------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_RELEASE_INIT.rst

@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_RELEASE_INIT
+-------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELEASE`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT.rst

@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT
+--------------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst

@@ -14,8 +14,10 @@ variables that must be set before CMake builds its first test project
 to check that the compiler for a language works.  It should not be
 used to load a file in cases that a normal :command:`include` will work.  Use
 it only as a last resort for behavior that cannot be achieved any
-other way.  For example, one may set ``CMAKE_C_FLAGS_INIT`` to change the
-default value used to initialize :variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>`
+other way.  For example, one may set the
+:variable:`CMAKE_C_FLAGS_INIT <CMAKE_<LANG>_FLAGS_INIT>` variable
+to change the default value used to initialize the
+:variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>` variable
 before it is cached.  The override file should NOT be used to set anything
 that could be set after languages are enabled, such as variables like
 :variable:`CMAKE_RUNTIME_OUTPUT_DIRECTORY` that affect the placement of

Modules/Compiler/ARMCC.cmake

@@ -20,11 +20,11 @@ set(CMAKE_AR "${CMAKE_ARMCC_AR}" CACHE FILEPATH "The ARMCC archiver" FORCE)
 mark_as_advanced(CMAKE_ARMCC_AR)
 
 macro(__compiler_armcc lang)
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Ospace -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-Otime -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Ospace -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -Otime -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 
   set(CMAKE_${lang}_OUTPUT_EXTENSION ".o")
   set(CMAKE_${lang}_OUTPUT_EXTENSION_REPLACE 1)

Modules/Compiler/Absoft-Fortran.cmake

@@ -1,8 +1,8 @@
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-YMOD_OUT_DIR=")
 set(CMAKE_Fortran_MODPATH_FLAG "-p")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")

Modules/Compiler/Bruce-C.cmake

@@ -1,7 +1,7 @@
 # Bruce C Compiler ignores "-g" flag and optimization cannot be
 # enabled here (it is implemented only for 8086 target).
-set (CMAKE_C_FLAGS_INIT "-D__CLASSIC_C__")
-set (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set (CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " -D__CLASSIC_C__")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")

Modules/Compiler/G95-Fortran.cmake

@@ -1,8 +1,8 @@
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-fmod=")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")

Modules/Compiler/GHS-C.cmake

@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_C_VERBOSE_FLAG "-v")
 set(CMAKE_C_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_C_FLAGS_INIT "")
-set(CMAKE_C_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_C_GHS_KERNEL_FLAGS_DEBUG_INIT "-ldebug ${CMAKE_C_FLAGS_DEBUG_INIT}")
 set(CMAKE_C_GHS_KERNEL_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT}")

Modules/Compiler/GHS-CXX.cmake

@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_CXX_VERBOSE_FLAG "-v")
 set(CMAKE_CXX_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_CXX_FLAGS_INIT "")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_CXX_FLAGS_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_CXX_GHS_KERNEL_FLAGS_DEBUG_INIT
   "-ldebug ${CMAKE_CXX_FLAGS_DEBUG_INIT}")

Modules/Compiler/GNU-Fortran.cmake

@@ -5,8 +5,8 @@ set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-ffree-form")
 
 # No -DNDEBUG for Fortran.
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
 
 # No -isystem for Fortran because it will not find .mod files.
 unset(CMAKE_INCLUDE_SYSTEM_FLAG_Fortran)

Modules/Compiler/GNU.cmake

@@ -45,11 +45,11 @@ macro(__compiler_gnu lang)
   endif()
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g -DNDEBUG")
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
   if(NOT APPLE OR NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 4) # work around #4462

Modules/Compiler/Intel.cmake

@@ -27,10 +27,10 @@ else()
   macro(__compiler_intel lang)
     set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
-    set(CMAKE_${lang}_FLAGS_INIT "")
-    set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-    set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os")
-    set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3")
-    set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+    string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+    string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+    string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os")
+    string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3")
+    string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
   endmacro()
 endif()

Modules/Compiler/PGI-C.cmake

@@ -1,4 +1,4 @@
 include(Compiler/PGI)
 __compiler_pgi(C)
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PGI-CXX.cmake

@@ -1,4 +1,4 @@
 include(Compiler/PGI)
 __compiler_pgi(CXX)
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PGI-Fortran.cmake

@@ -4,7 +4,7 @@ __compiler_pgi(Fortran)
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-Mnofreeform")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-Mfreeform")
 
-set(CMAKE_Fortran_FLAGS_INIT "${CMAKE_Fortran_FLAGS_INIT} -Mpreprocess -Kieee")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "${CMAKE_Fortran_FLAGS_DEBUG_INIT} -Mbounds")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " -Mpreprocess -Kieee")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -Mbounds")
 
 set(CMAKE_Fortran_MODDIR_FLAG "-module ")

Modules/Compiler/PGI.cmake

@@ -23,11 +23,11 @@ macro(__compiler_pgi lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g -O0")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O2 -s")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-fast -O3 -Mipa=fast")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -gopt")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g -O0")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O2 -s")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -fast -O3 -Mipa=fast")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -gopt")
 
   # Preprocessing and assembly rules.
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")

Modules/Compiler/PathScale-C.cmake

@@ -1,4 +1,4 @@
 include(Compiler/PathScale)
 __compiler_pathscale(C)
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PathScale-CXX.cmake

@@ -1,4 +1,4 @@
 include(Compiler/PathScale)
 __compiler_pathscale(CXX)
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PathScale.cmake

@@ -23,9 +23,9 @@ macro(__compiler_pathscale lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g -O0")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-g -O2")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g -O0")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -g -O2")
 endmacro()

Modules/Compiler/SunPro-ASM.cmake

@@ -8,11 +8,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_ASM_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_ASM_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_ASM_FLAG "-h")
 
-set(CMAKE_ASM_FLAGS_INIT "")
-set(CMAKE_ASM_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_ASM_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_INIT " ")
+string(APPEND CMAKE_ASM_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_ASM_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize ASM link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links

Modules/Compiler/SunPro-C.cmake

@@ -7,11 +7,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-h")
 
-set(CMAKE_C_FLAGS_INIT "")
-set(CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize C link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links

Modules/Compiler/SunPro-CXX.cmake

@@ -7,11 +7,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_CXX_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_CXX_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_CXX_FLAG "-h")
 
-set(CMAKE_CXX_FLAGS_INIT "")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize C link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links

Modules/Compiler/SunPro-Fortran.cmake

@@ -10,11 +10,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_Fortran_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_Fortran_FLAG "-h")
 set(CMAKE_EXECUTABLE_RUNTIME_Fortran_FLAG "-R")
 
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 set(CMAKE_Fortran_MODDIR_FLAG "-moddir=")
 set(CMAKE_Fortran_MODPATH_FLAG "-M")
 

Modules/Compiler/TinyCC-C.cmake

@@ -1,8 +1,8 @@
 set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")
 
 # no optimization in tcc:
-set (CMAKE_C_FLAGS_INIT "")
-set (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set (CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")

Modules/Compiler/XL-ASM.cmake

@@ -2,11 +2,11 @@ set(CMAKE_ASM_VERBOSE_FLAG "-V")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_ASM_FLAGS_INIT "-qthreaded -qhalt=e -qsourcetype=assembler")
+string(APPEND CMAKE_ASM_FLAGS_INIT " -qthreaded -qhalt=e -qsourcetype=assembler")
 
-set(CMAKE_ASM_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_ASM_FLAGS_RELEASE_INIT "-O -DNDEBUG")
-set(CMAKE_ASM_FLAGS_MINSIZEREL_INIT "-O -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_ASM_FLAGS_RELEASE_INIT " -O -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_MINSIZEREL_INIT " -O -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")
 
 set(CMAKE_ASM_SOURCE_FILE_EXTENSIONS s )

Modules/Compiler/XL-C.cmake

@@ -1,8 +1,8 @@
 include(Compiler/XL)
 __compiler_xl(C)
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_C_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_C_FLAGS_INIT " -qthreaded -qhalt=e")

Modules/Compiler/XL-CXX.cmake

@@ -1,11 +1,11 @@
 include(Compiler/XL)
 __compiler_xl(CXX)
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_CXX_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_CXX_FLAGS_INIT " -qthreaded -qhalt=e")
 
 set(CMAKE_CXX_COMPILE_OBJECT
   "<CMAKE_CXX_COMPILER> -+ <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -c <SOURCE>")

Modules/Compiler/XL-Fortran.cmake

@@ -10,7 +10,7 @@ set(CMAKE_Fortran_DEFINE_FLAG "-WF,-D")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_Fortran_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " -qthreaded -qhalt=e")
 
 # xlf: 1501-214 (W) command option E reserved for future use - ignored
 set(CMAKE_Fortran_CREATE_PREPROCESSED_SOURCE)

Modules/Compiler/XL.cmake

@@ -29,10 +29,10 @@ macro(__compiler_xl lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-V")
   set(CMAKE_${lang}_COMPILE_OPTIONS_PIC "-qpic")
 
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-g")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -g")
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE     "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
 

Modules/Platform/ARTOS-GNU-C.cmake

@@ -1,9 +1,9 @@
 # Define ARTOS to select proper behaviour and tell preprocessor to accept C++ style comments.
-set(CMAKE_C_FLAGS_INIT "-DARTOS -Xp -+")
+string(APPEND CMAKE_C_FLAGS_INIT " -DARTOS -Xp -+")
 # ac doesn't support -g properly and doesn't support the normal gcc optimization options. Just use the defaults set by ac.
-set(CMAKE_C_FLAGS_DEBUG_INIT "")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " ")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -DNDEBUG")
 # Most projects expect the stdio functions to be available.
 set(CMAKE_C_STANDARD_LIBRARIES_INIT "stdio.a")

Modules/Platform/Generic-ADSP-C.cmake

@@ -4,10 +4,10 @@ include(Platform/Generic-ADSP-Common)
 
 set(CMAKE_C_OUTPUT_EXTENSION ".doj")
 
-set(CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_C_FLAGS_RELEASE_INIT "")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " ")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " ")
 
 set(CMAKE_C_CREATE_STATIC_LIBRARY
     "<CMAKE_C_COMPILER> -build-lib -proc ${ADSP_PROCESSOR} -si-revision ${ADSP_PROCESSOR_SILICIUM_REVISION} -o <TARGET> <CMAKE_C_LINK_FLAGS> <OBJECTS>")

Modules/Platform/Generic-ADSP-CXX.cmake

@@ -2,10 +2,10 @@ include(Platform/Generic-ADSP-Common)
 
 set(CMAKE_CXX_OUTPUT_EXTENSION ".doj")
 
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " ")
 
 set(CMAKE_CXX_CREATE_STATIC_LIBRARY
      "<CMAKE_CXX_COMPILER> -build-lib -proc ${ADSP_PROCESSOR} -si-revision ${ADSP_PROCESSOR_SILICIUM_REVISION} -o <TARGET> <CMAKE_CXX_LINK_FLAGS> <OBJECTS>")

Modules/Platform/Generic-SDCC-C.cmake

@@ -30,7 +30,7 @@ set(CMAKE_AR "${SDCCLIB_EXECUTABLE}" CACHE FILEPATH "The sdcc librarian" FORCE)
 
 # CMAKE_C_FLAGS_INIT and CMAKE_EXE_LINKER_FLAGS_INIT should be set in a CMAKE_SYSTEM_PROCESSOR file
 if(NOT DEFINED CMAKE_C_FLAGS_INIT)
-  set(CMAKE_C_FLAGS_INIT "-mmcs51 --model-small")
+  string(APPEND CMAKE_C_FLAGS_INIT " -mmcs51 --model-small")
 endif()
 
 if(NOT DEFINED CMAKE_EXE_LINKER_FLAGS_INIT)

Modules/Platform/HP-UX-HP-CXX.cmake

@@ -8,7 +8,7 @@ set(CMAKE_CXX_CREATE_ASSEMBLY_SOURCE
   "rm -f `basename \"<SOURCE>\" | sed 's/\\.[^./]*$$//'`.o"
   )
 
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "+O3 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "+O2 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-g")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " +O3 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " +O2 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -g")

Modules/Platform/HP-UX-HP.cmake

@@ -27,7 +27,7 @@ macro(__hpux_compiler_hp lang)
   set(CMAKE_SHARED_LIBRARY_RUNTIME_${lang}_FLAG_SEP ":")
   set(CMAKE_SHARED_LIBRARY_SONAME_${lang}_FLAG "-Wl,+h")
 
-  set(CMAKE_${lang}_FLAGS_INIT "")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
 
   set(CMAKE_${lang}_LINK_FLAGS "-Wl,+s,+nodefaultrpath")
 endmacro()

Modules/Platform/Windows-Embarcadero.cmake

@@ -132,10 +132,10 @@ macro(__embarcadero_language lang)
     )
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "${_tM}")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-Od -v")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O1 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O2 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-Od")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_tM}")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -Od -v")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O1 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O2 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -Od")
   set(CMAKE_${lang}_STANDARD_LIBRARIES_INIT "import32.lib")
 endmacro()

Modules/Platform/Windows-Intel-Fortran.cmake

@@ -4,8 +4,8 @@ set(_COMPILE_Fortran " /fpp")
 set(CMAKE_Fortran_MODDIR_FLAG "-module:")
 set(CMAKE_Fortran_STANDARD_LIBRARIES_INIT "user32.lib")
 __windows_compiler_intel(Fortran)
-set (CMAKE_Fortran_FLAGS_INIT "/W1 /nologo /fpp /libs:dll /threads")
-set (CMAKE_Fortran_FLAGS_DEBUG_INIT "/Od /debug:full /dbglibs")
-set (CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "/O1 /DNDEBUG")
-set (CMAKE_Fortran_FLAGS_RELEASE_INIT "/O2 /DNDEBUG")
-set (CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "/O2 /debug:full /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " /W1 /nologo /fpp /libs:dll /threads")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " /Od /debug:full /dbglibs")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " /O1 /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " /O2 /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " /O2 /debug:full /DNDEBUG")

Modules/Platform/Windows-MSVC.cmake

@@ -303,17 +303,17 @@ macro(__windows_compiler_msvc lang)
     if(CMAKE_VS_PLATFORM_TOOLSET MATCHES "v[0-9]+_clang_.*")
       # note: MSVC 14 2015 Update 1 sets -fno-ms-compatibility by default, but this does not allow one to compile many projects
       # that include MS's own headers. CMake itself is affected project too.
-      set(CMAKE_${lang}_FLAGS_INIT "${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} -fms-extensions -fms-compatibility -D_WINDOWS -Wall${_FLAGS_${lang}}")
-      set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-D_DEBUG /MDd -gline-tables-only -fno-inline -O0 ${_RTC1}")
-      set(CMAKE_${lang}_FLAGS_RELEASE_INIT "/MD -O2 -DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "/MD -gline-tables-only -O2 -fno-inline -DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "/MD -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
+      string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} -fms-extensions -fms-compatibility -D_WINDOWS -Wall${_FLAGS_${lang}}")
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -D_DEBUG /MDd -gline-tables-only -fno-inline -O0 ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD -O2 -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD -gline-tables-only -O2 -fno-inline -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
     else()
-      set(CMAKE_${lang}_FLAGS_INIT "${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} /D_WINDOWS /W3${_FLAGS_${lang}}")
-      set(CMAKE_${lang}_FLAGS_DEBUG_INIT "/D_DEBUG /MDd /Zi /Ob0 /Od ${_RTC1}")
-      set(CMAKE_${lang}_FLAGS_RELEASE_INIT "/MD /O2 /Ob2 /DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "/MD /Zi /O2 /Ob1 /DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "/MD /O1 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} /D_WINDOWS /W3${_FLAGS_${lang}}")
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " /D_DEBUG /MDd /Zi /Ob0 /Od ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD /O2 /Ob2 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD /Zi /O2 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD /O1 /Ob1 /DNDEBUG")
     endif()
   endif()
   set(CMAKE_${lang}_LINKER_SUPPORTS_PDB ON)
@@ -323,7 +323,7 @@ macro(__windows_compiler_msvc lang)
     set(CMAKE_RC_COMPILER_INIT rc)
   endif()
   if(NOT CMAKE_RC_FLAGS_INIT)
-    set(CMAKE_RC_FLAGS_INIT "${_PLATFORM_DEFINES} ${_PLATFORM_DEFINES_${lang}}")
+    string(APPEND CMAKE_RC_FLAGS_INIT " ${_PLATFORM_DEFINES} ${_PLATFORM_DEFINES_${lang}}")
   endif()
 
   enable_language(RC)

Modules/Platform/Windows-OpenWatcom.cmake

@@ -52,13 +52,13 @@ set(CMAKE_BUILD_TYPE_INIT Debug)
 # single/multi-threaded                 /-bm
 # static/DLL run-time libraries         /-br
 # default is setup for multi-threaded + DLL run-time libraries
-set (CMAKE_C_FLAGS_INIT "-bt=nt -w3 -dWIN32 -br -bm")
-set (CMAKE_CXX_FLAGS_INIT "-bt=nt -xs -w3 -dWIN32 -br -bm")
+string(APPEND CMAKE_C_FLAGS_INIT " -bt=nt -w3 -dWIN32 -br -bm")
+string(APPEND CMAKE_CXX_FLAGS_INIT " -bt=nt -xs -w3 -dWIN32 -br -bm")
 foreach(lang C CXX)
-  set (CMAKE_${lang}_FLAGS_DEBUG_INIT "-d2")
-  set (CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-s -os -d0 -dNDEBUG")
-  set (CMAKE_${lang}_FLAGS_RELEASE_INIT "-s -ot -d0 -dNDEBUG")
-  set (CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-s -ot -d1 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -d2")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -s -os -d0 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -s -ot -d0 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -s -ot -d1 -dNDEBUG")
 endforeach()
 
 foreach(type CREATE_SHARED_LIBRARY CREATE_SHARED_MODULE LINK_EXECUTABLE)

Tests/RunCMake/ToolchainFile/FlagsInit-stdout.txt

@@ -0,0 +1,30 @@
+-- CMAKE_C_FLAGS='[^
+]*-DMY_FLAGS_INIT[^
+]*'
+-- CMAKE_C_FLAGS_DEBUG='[^
+]*-DMY_FLAGS_DEBUG_INIT[^
+]*'
+-- CMAKE_C_FLAGS_RELEASE='[^
+]*-DMY_FLAGS_RELEASE_INIT[^
+]*'
+-- CMAKE_C_FLAGS_MINSIZEREL='[^
+]*-DMY_FLAGS_MINSIZEREL_INIT[^
+]*'
+-- CMAKE_C_FLAGS_RELWITHDEBINFO='[^
+]*-DMY_FLAGS_RELWITHDEBINFO_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS='[^
+]*-DMY_FLAGS_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_DEBUG='[^
+]*-DMY_FLAGS_DEBUG_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_RELEASE='[^
+]*-DMY_FLAGS_RELEASE_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_MINSIZEREL='[^
+]*-DMY_FLAGS_MINSIZEREL_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_RELWITHDEBINFO='[^
+]*-DMY_FLAGS_RELWITHDEBINFO_INIT[^
+]*'

Tests/RunCMake/ToolchainFile/FlagsInit-toolchain.cmake

@@ -0,0 +1,7 @@
+foreach(lang C CXX)
+  set(CMAKE_${lang}_FLAGS_INIT -DMY_FLAGS_INIT)
+  set(CMAKE_${lang}_FLAGS_DEBUG_INIT -DMY_FLAGS_DEBUG_INIT)
+  set(CMAKE_${lang}_FLAGS_RELEASE_INIT -DMY_FLAGS_RELEASE_INIT)
+  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT -DMY_FLAGS_MINSIZEREL_INIT)
+  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT -DMY_FLAGS_RELWITHDEBINFO_INIT)
+endforeach()

Tests/RunCMake/ToolchainFile/FlagsInit.cmake

@@ -0,0 +1,7 @@
+enable_language(C)
+enable_language(CXX)
+foreach(lang C CXX)
+  foreach(c "" _DEBUG _RELEASE _MINSIZEREL _RELWITHDEBINFO)
+    message(STATUS "CMAKE_${lang}_FLAGS${c}='${CMAKE_${lang}_FLAGS${c}}'")
+  endforeach()
+endforeach()

Tests/RunCMake/ToolchainFile/RunCMakeTest.cmake

@@ -7,3 +7,4 @@ endfunction()
 
 run_cmake_toolchain(CallEnableLanguage)
 run_cmake_toolchain(CallProject)
+run_cmake_toolchain(FlagsInit)