The ddate command is called in src/clone/clone.c. Adding either sys-apps/util-linux[ddate(+)] or || ( sys-apps/util-linux[ddate] <sys-apps/util-linux-2.20 ) to RDEPEND should fix it. (It will require that the ebuild is bumped to at least EAPI 4 or EAPI 2, respectively.)
fixed in portage. thanks for the bug report.