Hi, dev-ml/uutf-1.0.0 needs dev-ml/uchar and should therefore depend on it.
indeed, thanks commit 78f805c1d4342ca6428a0c5d27874c37beffd9b2 Author: Alexis Ballier <aballier@gentoo.org> Date: Tue Nov 29 13:20:55 2016 +0100 dev-ml/uutf: add missing dep on uchar, bug #601172