Currently wireshark-0.99.6-r1 failes because of "-Werror" in combination with GCC 4.2. Adding "-Wno-error" should work. Like it did at: http://bugs.gentoo.org/show_bug.cgi?id=191538 Reproducible: Always
-Wno-error is not a solution. Upstream wants us to report such breakages. Please, attach full build output here, to speed up things.
Christoph, beside full build log, also show us emerge --info, please. Closing as NEEDINFO, as I did not mange to reproduce this bug on my system.