multilib-minimal inherits multilib-build and multilib-build inherits multilib, therefore inheriting just multilib-minimal is enough to get get_libdir() available i guess it would make sense to make multilib-minimal and multilib-build both acceptable to the QA check so it wouldn't complain about missing multilib temporarily threw this in where this came up: + 16 Mar 2013; Samuli Suominen <ssuominen@gentoo.org> libv4l-0.8.9-r1.ebuild: + Inherit multilib despite inheriting multilib-minimal to silence repoman + warning of get_libdir usage.
This is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=2e13ec014ffda81d340f3d373e879b9587078b0c
This is fixed in 2.1.11.56 and 2.2.0_alpha167.