The sys-freebsd/freebsd-lib-6.1 ebuild fails to apply the freebsd-lib-6.1-csu.amd64.patch as it cannot be found. In ${FILESDIR} there is a patch named freebsd-lib-6.1-csu-amd64.patch, however. So, I guess that either the ebuild needs to be fixed or the patch file needs to be renamed.
Fixed in cvs.