replaced line comments in public header.

include/SDL_opengl_glext.h

@@ -1,6 +1,6 @@
-// SDL modified the include guard to be compatible with Mesa and Apple include guards:
-// - Mesa uses: __gl_glext_h_
-// - Apple uses: __glext_h_
+/* SDL modified the include guard to be compatible with Mesa and Apple include guards:
+ * - Mesa uses: __gl_glext_h_
+ * - Apple uses: __glext_h_  */
 #if !defined(__glext_h_) && !defined(__gl_glext_h_)
 #define __glext_h_ 1
 #define __gl_glext_h_ 1