I have bumped up the gimp-1.3.21 ebuild. But I'm having same problems with the ebuild in portage.
if gcc -DHAVE_CONFIG_H -I. -I. -I../.. -I../.. -I../../app -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include -DG_LOG_DOMAIN=\"Gimp-Compositing\" -DG_DISABLE_DEPRECATED -DGDK_PIXBUF ...