Bug 246969 seems to have exposed an issue with 7.16.3 and bison-2.4, but 7.20.7 compiles fine on ~amd64 today. Please drop the version-specific dependency - thanks!
Forgot to note the bison version - compiles fine on ~amd64 with sys-devel/bison-2.4.1.
fixed in cvs, thanks for the report and fix. 28 Dec 2009; Markus Meier <maekke@gentoo.org> nip2-7.20.7.ebuild: relax =sys-devel/bison-2.3* dep to sys-devel/bison by dacook in bug #297984