See also bug #740262
The systemd service unit file is not included in source any more, it has to be added to the ebuild. It can be the same as the one in 8.2006.0, the last working verion:
# cat /lib/systemd/system/rsyslog.service
Description=System Logging Service
ExecStart=/usr/sbin/rsyslogd -n -iNONE
# Increase the default a bit in order to allow many simultaneous
# files to be monitored, we might need a lot of fds.
This one is now critical. The last systemd-working rsyslog release was removed from portage.
*** This bug has been marked as a duplicate of bug 740262 ***