x11-misc/xkeyboard-config is required for wlc compositors to function normally, as otherwise xkb context can't be initiated (see https://lists.freedesktop.org/archives/wayland-devel/2013-September/011177.html ). So it's necessary to add that as an RDEPEND.
I was traveling for a few days, and will not have access to my computer until tomorrow. I will fix this (and a few other issues with wlc) as soon as possible, when I get the chance. Thank you for reporting this.
Author: Jasen Borisov <tajjada@gmail.com> AuthorDate: Mon Jul 4 09:50:31 2016 +0300 Commit: Göktürk Yüksek <gokturk@gentoo.org> CommitDate: Thu Jul 7 22:52:07 2016 -0400 dev-libs/wlc: fix missing RDEPEND and X configuration Gentoo-Bug: 584462