Merge topic 'apple-isystem-gcc'

5b04aa31 Xcode: Disable test for system include dirs
2cae5128 Apple: Enable -isystem for GNU Compiler >= 4 (#15953)

Modules/Compiler/GNU.cmake

@@ -52,7 +52,7 @@ macro(__compiler_gnu lang)
   set(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_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
-  if(NOT APPLE)
+  if(NOT APPLE OR NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 4) # work around #4462
     set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-isystem ")
   endif()
 endmacro()

Tests/Complex/Executable/CMakeLists.txt

@@ -146,7 +146,8 @@ add_dependencies(notInAllCustom notInAllExe)
 #
 add_subdirectory(Temp)
 
-if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_INCLUDE_SYSTEM_FLAG_CXX)
+if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_INCLUDE_SYSTEM_FLAG_CXX
+   AND NOT XCODE) # XCODE is excluded due to #15687
   add_executable(testSystemDir testSystemDir.cxx)
   set_target_properties(testSystemDir PROPERTIES COMPILE_FLAGS "-Werror")
 endif()

Tests/ComplexOneConfig/Executable/CMakeLists.txt

@@ -146,7 +146,8 @@ add_dependencies(notInAllCustom notInAllExe)
 #
 add_subdirectory(Temp)
 
-if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_INCLUDE_SYSTEM_FLAG_CXX)
+if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_INCLUDE_SYSTEM_FLAG_CXX
+   AND NOT XCODE) # XCODE is excluded due to #15687
   add_executable(testSystemDir testSystemDir.cxx)
   set_target_properties(testSystemDir PROPERTIES COMPILE_FLAGS "-Werror")
 endif()