/usr/include/glib.h includes this file. It also contains a handy
description of what should be in the file -- glibconfig.h contains
architecture specific limits.
I can't seem to do any development without it.
(gimp-devel is included in redhat 6.1, but it's not in your component list,
so I used gimp)
It's in glib-devel, and seems to be there in the builds we have.