Hum, libxml v1 is deprecated, it not even part of the comps.xml as far as
I can tell and not installed. I think the package is dead at this point, it
is clearly obsolete, and shouldn't have been installed. On a recent 
install you don't get /usr/include/gnome-xml at all.
Not sure this is really a FC devel problem, maybe rather an upgrade transition
artefact, and I don't see how to fix it since the package seems to not being part
of Fedora Core devel at this point.

Daniel