[mutter] cogl: Fix build error when GL_ARB_sync is not defined

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

commit 6989fea76717b54496da829aca7ca5591ff36a52
Author: Andre Moreira Magalhaes <andre endlessm com>
Date:   Thu Mar 12 17:49:11 2020 -0300

    cogl: Fix build error when GL_ARB_sync is not defined
    
    Commit 41992757e0 introduced a change to use CoglContext.glFenceSync
    but this method is only available when GL_ARB_sync is defined (as
    defined on gl-prototypes/cogl-all-functions.h).
    
    This change fixes that.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1123

 cogl/cogl/driver/gl/gles/cogl-driver-gles.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/cogl/cogl/driver/gl/gles/cogl-driver-gles.c b/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
index e0c8ca1fa..ca98823e8 100644
--- a/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
+++ b/cogl/cogl/driver/gl/gles/cogl-driver-gles.c
@@ -366,8 +366,10 @@ _cogl_driver_update_features (CoglContext *context,
       _cogl_check_extension ("GL_OES_egl_sync", gl_extensions))
     COGL_FLAGS_SET (private_features, COGL_PRIVATE_FEATURE_OES_EGL_SYNC, TRUE);
 
+#ifdef GL_ARB_sync
   if (context->glFenceSync)
     COGL_FLAGS_SET (context->features, COGL_FEATURE_ID_FENCE, TRUE);
+#endif
 
   if (_cogl_check_extension ("GL_EXT_texture_rg", gl_extensions))
     COGL_FLAGS_SET (context->features,