[PATCH] unix: use libc-provided epoll_pwait wrapper

[PATCH] unix: use libc-provided epoll_pwait wrapper

Bug-Debian: https://bugs.debian.org/841354

Signed-off-by: Luca Bruno <lucab@debian.org>
We now use epoll_pwait() wrapper from libc, which takes care
of passing proper sigset_t size to kernel.

This is more portable, as some arch have a larger sigmask and
kernel explicitely checks size parameter to match sizeof(sigset_t).
Spotted as a uv_loop_configure regression on MIPS.

This fixes #335.

Many thanks to Tobias Leich who amended this
patch to fix #841354

Gbp-Pq: Name mips-epoll_pwait.diff