Your error might indicate that something with the com_err library went wrong. But I can't see what might have happened from the output you pasted and I would need the full build log.
You can either paste the log somewhere (e.g.
http://paste.lisp.org) or you go through a normal gentoo bug report and add "[kolab overlay]" to the summary. As cyrus_imapd-2.3.12_p2 is actually supposed to be going into the portage tree the latter might be better.
If you have sys-libs/com_err installed you should also add the installed version of the package.
Thanks for testing the newer package! It needs all testing it can get as I don't want to make a bad impression with the first version that includes the kolab patches

Cheers,
Gunnar