GDK dependency has been optional since poppler 0.8 and the API was deprecated in 0.16. I’ve just removed the GDK dependency in current git master so poppler 0.18 will only depend on glib and cairo.
If you are still using the GDK API, please port it to cairo before 0.18 (scheduled for June 27). GDK API in poppler 0.16 is just a wrapper around the cairo one, so you can even copy and paste the code if you still need to render into a GdkPixbuf.
If you need help, feel free to ask anything in poppler mailing list or #poppler channel in freenode.