Comment 1 for bug 1893021

The problem is with GTK function stubs being declared in the wrong sections in widget/gtk/mozgtk/mozgtk.c. Another recent upstream change did that too: https://phabricator.services.mozilla.com/D82804.

And this patch fixes it: https://bazaar.launchpad.net/~mozillateam/firefox/firefox.xenial/revision/1450