Nixos installs into a non-standard includedir, so need to take account of the 'includedir' option instead of just hard-coding 'include' here. https://bugzilla.gnome.org/show_bug.cgi?id=794856
Nixos installs into a non-standard includedir, so need to take account of the 'includedir' option instead of just hard-coding 'include' here. https://bugzilla.gnome.org/show_bug.cgi?id=794856