Bug 1611599 - gcc-10: Add an explicit include to glib.h r=stransky

Differential Revision: https://phabricator.services.mozilla.com/D61064

--HG--
extra : moz-landing-system : lando

widget/gtk/mozcontainer.cpp

@@ -6,6 +6,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozcontainer.h"
+#include <glib.h>
 #include <gtk/gtk.h>
 #include <gdk/gdkx.h>
 #ifdef MOZ_WAYLAND