[PATCH 2/3] Change sys/poll.h to poll.h

[Reagan Bohan]

Hi Kamil,

I am relatively inexperienced with email patches, so I appreciate your
patience.

> In what project is it emitting this?

musl libc installs sys/poll.h as a header which just includes poll.h and
emits a warning (with #warning), so each usage of sys/poll.h emits a
noisy compiler warning.

I will take the rest of your feedback into account and send a new patch
soon.