At least Mac OS X SDK 10.7 does not need that

(causes -Werror,-Wunused-macros, rather)

Change-Id: Ic8449c7794739033ddf1f6227f025ce4a0c899d0

slideshow/source/engine/OGLTrans/mac/OGLTrans_TransitionerImpl.mm

@@ -26,7 +26,11 @@
  *
  ************************************************************************/
 
+#include "sal/config.h"
+
+#if MACOSX_SDK_VERSION < 1070
 #define GLX_GLXEXT_PROTOTYPES 1
+#endif
 #include "OGLTrans_TransitionImpl.hxx"
 
 #include <com/sun/star/beans/XFastPropertySet.hpp>