A cleaner way to fix up those deprecations.
Fix double-free crash if last menu item is a separator.
Get Enable/Disable working again

1278ca1aa2 fixed https://bugzilla.gnome.org/show_bug.cgi?id=703781
by replacing the implementation of setEnabled to set or remove the
activation item, making use of NSMenu's AutoenablesItems feature
to enable and disable menu items. This feature was turned off for
menus generated from GtkMenus. Remove that.
Enable BUILT_UI in test-integration while suppressing gtk deprecated warnings