Fix compilation for .m files extension

CMakeLists.txt

@@ -3224,6 +3224,15 @@ if(PS2)
   target_compile_options(sdl-build-options INTERFACE "-Wno-error=declaration-after-statement")
 endif()
 
+if(APPLE)
+  foreach(SOURCE_FILE ${SOURCE_FILES})
+    get_filename_component(FILE_EXTENSION ${SOURCE_FILE} EXT)
+    if(FILE_EXTENSION STREQUAL "m")
+      set_property(SOURCE ${SOURCE_FILE} APPEND_STRING PROPERTY COMPILE_FLAGS " -x objective-c")
+    endif()
+  endforeach()
+endif()
+
 if(SDL_SHARED)
   add_library(SDL2 SHARED ${SOURCE_FILES} ${VERSION_SOURCES})
   add_dependencies(SDL2 sdl_headers_copy)