This was [changed upstream](https://github.com/GNOME/devhelp/commit/94f3661dbc3d0a228a78ff4a4d38b076b7a2...) some unknown time ago.
I didn't really test this properly, hoping Travis CI will do it for me :) You can view, comment on, or merge this pull request online at:
https://github.com/geany/geany-plugins/pull/878
-- Commit Summary --
* Devhelp: Fix embedded library's use of glib-genmarshal
-- File Changes --
M devhelp/devhelp/Makefile.am (5)
-- Patch Links --
https://github.com/geany/geany-plugins/pull/878.patch https://github.com/geany/geany-plugins/pull/878.diff