Define SDL_PLATFORM_* macros instead of underscored ones (#8875)

VisualC-GDK/tests/testgdk/src/testgdk.cpp

@@ -311,7 +311,7 @@ loop()
         if (event.type == SDL_EVENT_KEY_DOWN && !event.key.repeat) {
             SDL_Log("Initial SDL_EVENT_KEY_DOWN: %s", SDL_GetScancodeName(event.key.keysym.scancode));
         }
-#if defined(__XBOXONE__) || defined(__XBOXSERIES__)
+#if defined(SDL_PLATFORM_XBOXONE) || defined(SDL_PLATFORM_XBOXSERIES)
         /* On Xbox, ignore the keydown event because the features aren't supported */
         if (event.type != SDL_EVENT_KEY_DOWN) {
             SDLTest_CommonEvent(state, &event, &done);