The configure script enables epoll by default if the system call is available via the sys/epoll.h header. For some reason, the ebuild overrides this auto-detection and exposes it via a use flag. epoll has been available since Linux 2.5.44 and glibc-2.3.2. Please set IUSE="+epoll" in the ebuild, or remove the use flag and let the configure script auto-detect it. I think the latter would be preferable. This feature is required by sys-apps/systemd[http].
done.