Add some defines that are missing on GLES

The GLES2 driver wasn't compiling unless the GL driver is also enabled
because some run-time conditional code was directly using GL-only
defines.

This should also fix compiling using the stock GL headers on OS X
which don't define GL_NUM_EXTENSIONS.

https://bugzilla.gnome.org/show_bug.cgi?id=692420

Reviewed-by: Robert Bragg <robert@linux.intel.com>

(cherry picked from commit 661e1719aa0b95c409c568ec91ea52b8ff90519b)

cogl/cogl-context.c

@@ -58,11 +58,15 @@
 #include "cogl-pipeline-fragend-arbfp-private.h"
 #endif
 
-/* This isn't defined in the GLES headers */
+/* These aren't defined in the GLES headers */
 #ifndef GL_POINT_SPRITE
 #define GL_POINT_SPRITE 0x8861
 #endif
 
+#ifndef GL_NUM_EXTENSIONS
+#define GL_NUM_EXTENSIONS 0x821D
+#endif
+
 static void _cogl_context_free (CoglContext *context);
 
 COGL_OBJECT_DEFINE (Context, context);
@@ -649,6 +653,7 @@ _cogl_context_get_gl_extensions (CoglContext *context)
 
   /* In GL 3, querying GL_EXTENSIONS is deprecated so we have to build
    * the array using glGetStringi instead */
+#ifdef HAVE_COGL_GL
   if (context->driver == COGL_DRIVER_GL3)
     {
       int num_extensions, i;
@@ -667,6 +672,7 @@ _cogl_context_get_gl_extensions (CoglContext *context)
       ret[num_extensions] = NULL;
     }
   else
+#endif
     {
       const char *all_extensions =
         (const char *) context->glGetString (GL_EXTENSIONS);

cogl/cogl-texture.c

@@ -61,6 +61,11 @@
 #include <stdlib.h>
 #include <math.h>
 
+/* This isn't defined in the GLES headers */
+#ifndef GL_RED
+#define GL_RED 0x1903
+#endif
+
 uint32_t
 cogl_texture_error_quark (void)
 {