Created attachment 2951 Patch which adds the explicit linking The gtkdocs program does not explicitly link against glib/gobject.
Could you attach clean patches (seen other bugs too about this), only the change to Makefile.am is relevant.
Pushed in 24b7053. Next time only attach a patch with the relevant changes.
Oops, sorry about that Nick. I had intended to do just that, but must have committed everything by mistake.