codegen: Include "glib.h" for g_return_*() usage
codegen: Include "glib.h" for g_return_*() usage

Fixes https://gitlab.gnome.org/GNOME/vala/issues/940

GNOME/vala,GNOME/vala,frida/vala,GNOME/vala,frida/vala,frida/vala,frida/vala,GNOME/vala,frida/vala