POSIX.1-2001 and POSIX.1-2008 specifies include <poll.h> so use that rather than the non-standard/legacy include <sys/poll.h>.
This fixes the following warnings when building with musl libc:
1 | #warning redirecting incorrect #include <sys/poll.h> to <poll.h>
| ^~~~~~~We keep include <sys/poll.h> as fallback incase AIX has not yet adjusted to POSIX.1-2001.
Signed-off-by: Natanael Copa ncopa@alpinelinux.org