[pypy-issue] Issue #2607: Recommended include path for poll.h (pypy/pypy)

[Jean-Louis Fuchs]

New issue 2607: Recommended include path for poll.h
https://bitbucket.org/pypy/pypy/issues/2607/recommended-include-path-for-pollh

Jean-Louis Fuchs:

musl libc recommends including poll.h instead of sys/poll.h (usually the do this because it is defined in POSIX)

```
#!bash

$> cat /usr/include/sys/poll.h
#warning redirecting incorrect #include <sys/poll.h> to <poll.h>
#include <poll.h>
```

The patch is tested with PyPy3.5 v5.8.0