Add libepoll-shim to the ports tree

small epoll implementation using kqueue; includes all features needed for
libinput/libevdev

The project was initially created here:
https://github.com/jiixyj/epoll-shim/

Forked and expected on the FreeBSDDesktop github
https://github.com/FreeBSDDesktop/epoll-shim

It is required for Wayland import

Submitted by: Johannes Lundberg <yohanesu75@gmail.com>