This has been an ongoing issue since July that I've worked around in the past by forcing various packages to compile against mariadb-connector-c, but with the latest updates, I've tried again to use the existing packages. The issue is zoneminder core dumps with mysql-connector-c. Installing the current zoneminder (www-misc/zoneminder-1.30.4-r1) with the current mysql-connector-c (dev-db/mysql-connector-c-6.1.11-r1) causes zmc and various other zoneminder programs to segfault.
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=c66a9574205fcefe13c0b13a778af774f2703a0b