app-editors/zile-2.4.7 was marked -x86-fbsd with ChangeLog entry "Drop ~x86-fbsd. boehm-gc not yet keyworded." However, a keyword still missing from a dependency is not a sufficient reason for marking an ebuild as -arch. Policy reference: <http://devmanual.gentoo.org/keywording/>
It seems I'd misused ekeyword. Dropped -x86-fbsd.