ENH: make supporting embedded compilers need a user specific linker file for

compiling an executable (amd thus cannot build the compiler-id program)
easier by providing CMAKE_FORCE_XXX() macros which force cmake to use the
given compilers anyway

Alex

Modules/CMakeForceCompiler.cmake

@@ -0,0 +1,51 @@
+
+# These are macros intended to be used only when crosscompiling in the 
+# toolchain-file and only if the compiler is not able to link an 
+# executable by default (usually because they need user-specific 
+# linker files which describe the layout of the target memory).
+#
+# It offers the following macros:
+#
+# macro CMAKE_FORCE_SYSTEM(name version processor)
+#   Set CMAKE_SYSTEM_NAME, CMAKE_SYSTEM_VERSION and CMAKE_SYSTEM_PROCESSOR
+#
+# macro CMAKE_FORCE_C_COMPILER(compiler compiler_id sizeof_void)
+#   Set CMAKE_C_COMPILER to the given compiler and set CMAKE_C_COMPILER_ID
+#   to the given compiler_id. This Id is used by cmake to construct the filename
+#   of the system-compiler.cmake file. For C also the size of a void-pointer
+#   has to be predefined.
+#
+# macro CMAKE_FORCE_CXX_COMPILER(compiler compiler_id)
+#   The same as CMAKE_FORCE_C_COMPILER, but for CXX. Here the size of 
+#   the void pointer is not requried.
+#
+# So a simple toolchain file could look like this:
+#
+# INCLUDE (CMakeForceCompiler)
+# CMAKE_FORCE_SYSTEM ("Generic"   "0.0"   "hc12")
+# CMAKE_FORCE_C_COMPILER   (chc12 FreescaleCHC12  2)
+# CMAKE_FORCE_CXX_COMPILER (chc12 FreescaleCHC12)
+
+
+MACRO(CMAKE_FORCE_SYSTEM name version proc)
+   SET(CMAKE_SYSTEM_NAME "${name}")
+   SET(CMAKE_SYSTEM_VERSION "${version}")
+   SET(CMAKE_SYSTEM_PROCESSOR "${proc}")
+ENDMACRO(CMAKE_FORCE_SYSTEM)
+
+MACRO(CMAKE_FORCE_C_COMPILER compiler id sizeof_void)
+  SET(CMAKE_C_COMPILER "${compiler}")
+  SET(CMAKE_C_COMPILER_ID_RUN TRUE)
+  SET(CMAKE_C_COMPILER_ID ${id})
+  SET(CMAKE_C_COMPILER_WORKS TRUE)
+  SET(CMAKE_SIZEOF_VOID_P ${sizeof_void} CACHE STRING "sizeof void")
+  SET(HAVE_CMAKE_SIZEOF_VOID_P TRUE CACHE INTERNAL "have sizeof void")
+ENDMACRO(CMAKE_FORCE_C_COMPILER)
+
+MACRO(CMAKE_FORCE_CXX_COMPILER compiler id)
+  SET(CMAKE_CXX_COMPILER "${compiler}")
+  SET(CMAKE_CXX_COMPILER_ID_RUN TRUE)
+  SET(CMAKE_CXX_COMPILER_ID ${id})
+  SET(CMAKE_CXX_COMPILER_WORKS TRUE)
+ENDMACRO(CMAKE_FORCE_CXX_COMPILER)
+