Since the migration to /usr/lib root-prefix for systemd the pam_systemd module is incorrectly installed to /usr/lib as well. Please pass --with-pamlibdir to configure in the systemd ebuilds. btw: Other directories like the udevulesdir and dbusdirs are detected by the configure script since it uses pkg-config there. Not sure, but I think since thats automagic, the ebuild should pass those explicitly as well? Reproducible: Always
This is fixed already in -9999.
Fixed in all current versions (with revision bumps).