The ebuilds for pam_mysql call make DESTDIR=${D} install || die directly and are breakting multilib-strict-support on amd64. Changing that line to einstall helps out. I noticed, that the einstall-modified version installs to /usr/lib64 instead of /lib64/security/ where it should according to the PAM docs.
make install is fine, we just have to add the LIBDIR var, I guess
*** Bug 144799 has been marked as a duplicate of this bug. ***
10 Aug 2006; Danny van Dyk <kugelfang@gentoo.org> pam_mysql-0.7_rc1-r1.ebuild: Fixed bug #138986 (multilib-strict). Kugenfang, the fix is missing inherit multilib, so it installs into / now :(
23 Aug 2006; Danny van Dyk <kugelfang@gentoo.org> pam_mysql-0.7_rc1-r1.ebuild: Forgot to add multilib.eclass to the inherit line.