build: Explicitly link to gmodule-2.0
build: Explicitly link to gmodule-2.0

Recent changes in glib-2.32 deps in pkg-config files require addition of
gmodule-2.0 to PKG_CHECK_MODULES. This underlinking will be visible when
using gold linker.

https://bugzilla.gnome.org/show_bug.cgi?id=677616

GNOME/gnome-panel,GNOME/gnome-panel