Windows GDK Support (#5830)

* Added GDK

* Simplfied checks in SDL_config_wingdk.h

* Added testgdk sample

* Added GDK readme

* Fixed error in merge of SDL_windows.h

* Additional GDK fixes

* OpenWatcom should not export _SDL_GDKGetTaskQueue

* Formatting fixes

* Moved initialization code into SDL_GDKRunApp

test/testsprite2.c

@@ -56,7 +56,12 @@ quit(int rc)
     SDL_free(positions);
     SDL_free(velocities);
     SDLTest_CommonQuit(state);
-    exit(rc);
+    /* If rc is 0, just let main return normally rather than calling exit.
+     * This allows testing of platforms where SDL_main is required and does meaningful cleanup.
+     */
+    if (rc != 0) {
+        exit(rc);
+    }
 }
 
 int