Replace USE_LOCAL_HEADERS with USE_INTERNAL_*

code/renderergl2/tr_extensions.c

@@ -21,7 +21,7 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 // tr_extensions.c - extensions needed by the renderer not in sdl_glimp.c
 
-#ifdef USE_LOCAL_HEADERS
+#ifdef USE_INTERNAL_SDL_HEADERS
 #	include "SDL.h"
 #else
 #	include <SDL.h>