eventfd(2) and timerfd(2) APIs

[Jason Thorpe]

Last year, I wrote implementations of the Linux eventfd(2) and timerfd(2) 
interfaces for NetBSD, with the goal of improving our Linux emulation.  In 
order to be able to test them with ATF tests, I went ahead and made them native 
calls as well.

Here are the man pages describing the interfaces:

        https://www.netbsd.org/~thorpej/eventfd.2
        https://www.netbsd.org/~thorpej/timerfd.2

Any objections to adding these?

-- thorpej