CMake: fix set_optimization_flags() (issue #185)

Author: Morwenn

cmake/functions/project_flags.cmake

@@ -65,20 +65,20 @@ macro(set_optimization_flags)
     if (NOT OPTIMIZATION_FLAG_IS_SET)
         if (CMAKE_BUILD_TYPE STREQUAL "Debug")
             if (EMSCRIPTEN)
-                list(APPEND CMAKE_CXX_FLAGS " -O0 -g4")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O0 -g4")
             elseif (MSVC)
-                list(APPEND CMAKE_CXX_FLAGS " /O0")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /O0")
             elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
-                list(APPEND CMAKE_CXX_FLAGS " -O0")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O0")
             else()
                 # https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
-                list(APPEND CMAKE_CXX_FLAGS " -Og")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Og")
             endif()
         else()
             if (MSVC)
-                list(APPEND CMAKE_CXX_FLAGS " /O2")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /O2")
             else()
-                list(APPEND CMAKE_CXX_FLAGS " -O2")
+                set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2")
             endif()
         endif()
         message("Setting CXX flags to default for ${CMAKE_BUILD_TYPE} mode (${CMAKE_CXX_FLAGS})")