Add libxml-2.0 to libvirt-gconfig-1.0.pc
Add libxml-2.0 to libvirt-gconfig-1.0.pc

The libvirt-gconfig header files depend on the libxml header
files, so this must be expressed in the pkgconfig file to
ensure the include path for libxml2 gets added to the compiler
args

libvirt/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib,JGulic/libvirt-glib,JGulic/libvirt-glib