F23 has split gdk-pixbuf2-devel >= 2.31.3-5 into 3 packages, gdk-pixbuf2-devel,
gdk-pixbuf2-modules-devel, and gdk-pixbuf2-xlib-devel. gtk2-devel does not depend
on gdk-pixbuf2-xlib-devel. Therefore, we need to pull in gdk-pixbuf2-xlib-devel
dependency ourselves.