Fix missing USE_INTERNAL_SDL_HEADERS definitions

cmake/libraries/sdl.cmake

@@ -9,6 +9,8 @@ endif()
 
 if(USE_INTERNAL_SDL AND HAVE_INTERNAL_SDL)
     set(SDL2_INCLUDE_DIRS ${INTERNAL_SDL_DIR}/include)
+    list(APPEND CLIENT_DEFINITIONS USE_INTERNAL_SDL_HEADERS)
+    list(APPEND RENDERER_DEFINITIONS USE_INTERNAL_SDL_HEADERS)
 
     if(WIN32)
         if(ARCH STREQUAL "x86_64")