Unless app-text/rman is installed, emake will fail when emerging x11-terms/root-tail. Thus, rman should be pulled in as a dependency, but at the moment it is not.
It's not missing rman dependency, read the ebuild. Also virtual-x11/7.0-r2 depends on rman. No way to miss the dependency unless you are messing with virtuals in /etc/portage. Not a bug, closing.