Improve logging performance and make log priorities thread-safe

Fixes https://github.com/libsdl-org/SDL/issues/9679

test/testrendercopyex.c

@@ -124,9 +124,6 @@ int main(int argc, char *argv[])
         return 1;
     }
 
-    /* Enable standard application logging */
-    SDL_SetLogPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);
-
     if (!SDLTest_CommonDefaultArgs(state, argc, argv) || !SDLTest_CommonInit(state)) {
         SDLTest_CommonQuit(state);
         return 1;