Improve logging performance and make log priorities thread-safe

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

test/testmodal.c

@@ -31,9 +31,6 @@ int main(int argc, char *argv[])
         return 1;
     }
 
-    /* Enable standard application logging */
-    SDL_SetLogPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);
-
     /* Parse commandline */
     for (i = 1; i < argc;) {
         int consumed;