Make internal SDL sources include SDL_internal.h instead of SDL_config.h

The new header will include SDL_config.h, but allows for other global stuff.

src/audio/sun/SDL_sunaudio.h

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_config.h"
+#include "../../SDL_internal.h"
 
 #ifndef _SDL_sunaudio_h
 #define _SDL_sunaudio_h