The dev-java/icedtea build system is quite complicated, targeted to Linux, and on top of that has tons of build dependencies which are not runtime dependencies, including X, cups and ALSA. Per https://bugs.gentoo.org/show_bug.cgi?id=409901#c2 "upstream doesn't see this as a priority" so it will be several years before icedtea can be built sanely on any platform.
Meanwhile ryao pointed to the FreeBSD upstream port for OpenJDK at http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/ports/java/openjdk6/Makefile?rev=1.64;content-type=text%2Fplain and mentioned the idea to convert this into an ebuild for Gentoo/BSD, which could possibly be more sane. Maybe it could even end up replacing icedtea for Gentoo in general, if it turns out that the approach used in the port file fits better with how Portage works, which I find not too unlikely.
A JRE on my Gentoo/BSD system without a million dependencies.
*-fbsd is gone.