Improve logging performance and make log priorities thread-safe

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

test/torturethread.c

@@ -89,15 +89,6 @@ int main(int argc, char *argv[])
         return 1;
     }
 
-    /* Enable standard application logging */
-    SDL_SetLogPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);
-
-    /* Load the SDL library */
-    if (!SDL_Init(0)) {
-        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s\n", SDL_GetError());
-        return 1;
-    }
-
     if (!SDLTest_CommonDefaultArgs(state, argc, argv)) {
         SDL_Quit();
         SDLTest_CommonDestroyState(state);