CMake: only add compiler flags that are actually compatible with the compiler…

CMake: only add compiler flags that are actually compatible with the compiler being used - the compiler detection logic in the Makefile is not perfect and that sometime results in weird conflicts

CMakeLists.txt

 cmake_minimum_required(VERSION 2.8.12)
 
+include(CMakeParseArguments)
+include(CheckCCompilerFlag)
+
+# filter out flags that are not appropriate for the compiler used
+function(target_compile_options_filtered target visibility)
+    foreach( flag ${ARGN} )
+        if( flag MATCHES "^-D.*" )
+            target_compile_options( ${target} ${visibility} ${flag} )
+        else()
+            check_c_compiler_flag( ${flag} COMPILER_SUPPORTS__${flag} )
+            if( COMPILER_SUPPORTS__${flag} )
+                target_compile_options( ${target} ${visibility} ${flag} )
+            endif()
+        endif()
+    endforeach()
+endfunction()
+
 project(abc)
 
+# run make to extract compiler options, linker options and list of source files
 execute_process(
-  COMMAND make ABC_MAKE_NO_DEPS=1 cmake_info
+  COMMAND make ABC_MAKE_NO_DEPS=1 CC=${CMAKE_C_COMPILER} CXX=${CMAKE_CXX_COMPILER} LD=${CMAKE_CXX_COMPILER} cmake_info
   WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
   OUTPUT_VARIABLE MAKE_OUTPUT
 )
@@ -26,5 +44,5 @@ extract_var(SEPARATOR_CFLAGS ABC_CFLAGS ${MAKE_OUTPUT})
 add_executable(abc ${ABC_SRC})
 
 target_include_directories(abc PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src )
-target_compile_options(abc PRIVATE ${ABC_CFLAGS} )
+target_compile_options_filtered(abc PRIVATE ${ABC_CFLAGS} -Wno-unused-but-set-variable )
 target_link_libraries(abc PRIVATE ${ABC_LIBS})