This is due to libintl.h NOT including locale.h when not building at least at -O1, see http://blog.flameeyes.eu/2008/09/02/testing-the-corner-cases for more information about the problem.
+ 20 Jun 2012; Justin Lecher <jlec@gentoo.org> authforce-0.9.9-r1.ebuild, + +files/authforce-0.9.9-locale.patch, metadata.xml: + Fix missing include which disaalowed O0 builds, #240740 +