Multilib stuff added by mgorny causes a conflict when the system is updated:

WARNING: One or more updates have been skipped due to a dependency conflict:

sys-libs/pam:0

(sys-libs/pam-1.1.6-r4::funtoo-overlay, ebuild scheduled for merge) conflicts with
>=sys-libs/pam-0.78[abi_x86_64(-)] required by (virtual/pam-0-r1::gentoo, ebuild scheduled for merge)

This is on a pure64 system but also impacts multilib systems. Suggested fix is to fork virtual/pam and remove 0-r1.