Move the fallback define for GL_PACK_INVERT_MESA

The if-undefined fallback declaration for GL_PACK_INVERT_MESA was
originally added in cogl.c along with code to use it (as part of commit
6f79eb8a5a).  Later on, commit
10a38bb14f moved the code that used it to
cogl-framebuffer.c but didn't move the define along with it.  Do that
now.

https://bugzilla.gnome.org/show_bug.cgi?id=672038

Reviewed-by: Neil Roberts <neil@linux.intel.com>

cogl/cogl-framebuffer.c

@@ -104,6 +104,10 @@
 #ifndef GL_TEXTURE_SAMPLES_IMG
 #define GL_TEXTURE_SAMPLES_IMG            0x9136
 #endif
+#ifndef GL_PACK_INVERT_MESA
+#define GL_PACK_INVERT_MESA 0x8758
+#endif
+
 
 typedef enum {
   _TRY_DEPTH_STENCIL    = 1L<<0,

cogl/cogl.c

@@ -51,10 +51,6 @@
 #include "cogl1-context.h"
 #include "cogl-offscreen.h"
 
-#ifndef GL_PACK_INVERT_MESA
-#define GL_PACK_INVERT_MESA 0x8758
-#endif
-
 #ifdef COGL_GL_DEBUG
 /* GL error to string conversion */
 static const struct {