getting closer...

$ grep glib *.c
polkit-authorization.c:#include <glib.h>
polkit-authorization-db.c:#include <glib.h>
polkit-authorization-db-dummy.c:#include <glib.h>
polkit-config.c:#include <glib.h>
polkit-context.c:#include <glib.h>
polkit-sysdeps.c:#include <glib.h>