gl: fix broken build due to previous commit 2fd84a6c

Can reproduce after installing libgraphene-dev

Also fixes caopengllayersink.h to anticipate build error on osx.

https://bugzilla.gnome.org/show_bug.cgi?id=784779

ext/gl/caopengllayersink.h

@@ -26,6 +26,7 @@
 #include <gst/video/video.h>
 
 #include <gst/gl/gl.h>
+#include <gst/gl/gstglfuncs.h>
 #include <gst/gl/cocoa/gstglcaopengllayer.h>
 
 G_BEGIN_DECLS

ext/gl/gstgltransformation.h

@@ -22,6 +22,7 @@
 #define _GST_GL_TRANSFORMATION_H_
 
 #include <gst/gl/gstglfilter.h>
+#include <gst/gl/gstglfuncs.h>
 #include <graphene.h>
 
 G_BEGIN_DECLS