The summary says it all: The ebuild calls configure with --disable-use-mb, but the configure option is actually called --disable-mb .
Fixed. Thanks for reporting and for the fix. --- ChangeLog 2013-03-26 14:51:18.353221979 +0100 +++ ChangeLog.new 2013-03-26 14:51:23.969118512 +0100 @@ -2,6 +2,9 @@ # Copyright 1999-2013 Gentoo Foundation; Distributed under the GPL v2 # $Header: /var/cvsroot/gentoo-x86/x11-misc/xlockmore/ChangeLog,v 1.126 2013/03/23 16:46:59 jer Exp $ + 26 Mar 2013; Jeroen Roovers <jer@gentoo.org> xlockmore-5.42.ebuild: + --disable-use-mb -> --disable-mb by Klaus Kusche (bug #463246).