Please, change dependency x11-themes/gtk-engines-nimbus into x11-themes/nimbus The former packages is no longer in portage; the latter provide both the theme and its engine. Also, "x11-themes/gtk-engines-quartz" doesn't compile (hard masked, BTW)... maybe this dep should be removed.
gtk-engines-meta isn't a package in the main Gentoo repo, where does it come from?
Ouch, wrong tracker: it's a Funtoo package ^_^. Sorry!