include(CheckCCompilerFlag) function(enable_c_compiler_flag_if_supported flag) string(FIND "${CMAKE_C_FLAGS}" "${flag}" flag_already_set) if (flag_already_set EQUAL -1) check_c_compiler_flag("${flag}" flag_supported) if (flag_supported) set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${flag}" PARENT_SCOPE) endif () unset(flag_supported CACHE) endif () endfunction ()