pangox was removed from gtkglext's git repository with the commit https://mail.gnome.org/archives/commits-list/2010-October/msg03446.html
The old repository is gone but there is a gtk3 port which has the complete unchanged history, including that commit: https://github.com/tdz/gtkglext/commit/32f37c936691baa25cc463c5339d0754bbaed8dc Importing this version might be a way forward. It is not ABI compatible with 1.2.0 though.
