Fix loading of PNG resources on big-endian machines

LodePNG always loads PNG in big-endian RGBA format. For this reason,
when loading PNG files VVVVVV was specifying the format as ABGR and the
conversion would then be performed by SDL. However, then running on
big-endian machines, this conversion should not be performed at all, and
the surface format should then be set to RGBA.

desktop_version/src/GraphicsResources.cpp

@@ -65,7 +65,11 @@ static SDL_Surface* LoadImageRaw(const char* filename, unsigned char** data)
         height,
         32,
         width * 4,
+#if SDL_BYTEORDER == SDL_BIG_ENDIAN
+        SDL_PIXELFORMAT_RGBA8888
+#else
         SDL_PIXELFORMAT_ABGR8888
+#endif
     );
 
     return loadedImage;