[libvirt] building xen and libvirt with odd --prefix fails

My xen is configured with "--prefix=/odd/path --enable-rpath". My libvirt is configured with "env PKG_CONFIG_PATH=/odd/path/share/pkgconfig bash -x autogen.sh --without-xen --with-libxl". Now make in libvirt fails to find "xen/xen.h" needed by xenconfig/xen_common.c, I think it expects it in /usr/include. But I have no xen-devel.rpm installed. I wonder if there are wrong assumptions in libvirt about xen. Since a while xen has a xenlight.pc which contains the required info to find headers and libs. Can there ever be a case where libxl is somewhere else than libxenstore and whatever else is provided by xen? I think they always go into the very same place. So shouldnt libvirt be updated to first check for xenlight.pc, and use the result for everything related to xen? I think that would work for every xen version which has a xenlight.pc (4.5+). And initially I did not pass the matching --prefix to libvirts configure. Even with matching --prefix libvirt does not look in $prefix/include for xen/xen.h, even with --includedir=$prefix/include. Olaf