[mutter] cogl-gles2/Makefile.am: Add cogl/ includedir

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit da741ead258bd2cf6f18dbd0a8cb78ad80b7ed13
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu May 24 17:15:23 2018 +0200

    cogl-gles2/Makefile.am: Add cogl/ includedir
    
    Otherwise cogl-egl-defines.h isn't found when building out-of-tree.

 cogl/cogl-gles2/Makefile.am | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/cogl/cogl-gles2/Makefile.am b/cogl/cogl-gles2/Makefile.am
index 294228d7a..4cba75bbe 100644
--- a/cogl/cogl-gles2/Makefile.am
+++ b/cogl/cogl-gles2/Makefile.am
@@ -9,7 +9,9 @@ mutterlib_LTLIBRARIES = libmutter-cogl-gles2-@LIBMUTTER_API_VERSION@.la
 
 AM_CPPFLAGS = \
        -I$(top_srcdir) \
-       -I$(top_builddir)
+       -I$(top_builddir) \
+       -I$(top_builddir)/cogl \
+       $(NULL)
 
 AM_CFLAGS = $(COGL_DEP_CFLAGS) $(COGL_EXTRA_CFLAGS) $(MAINTAINER_CFLAGS)