unix: add Poll for linux

Change-Id: I273bd852f85d204694872a1615be51dc027b97ee
Reviewed-on: https://go-review.googlesource.com/23661
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_linux.go

@@ -60,6 +60,15 @@ func Openat(dirfd int, path string, flags int, mode uint32) (fd int, err error)
 	return openat(dirfd, path, flags|O_LARGEFILE, mode)
 }
 
+//sys	poll(fds *PollFd, nfd int, timeout int) (n int, err error)
+
+func Poll(fds []PollFd, timeout int) (n int, err error) {
+	if len(fds) == 0 {
+		return poll(nil, 0, timeout)
+	}
+	return poll(&fds[0], len(fds), timeout)
+}
+
 //sys	readlinkat(dirfd int, path string, buf []byte) (n int, err error)
 
 func Readlink(path string, buf []byte) (n int, err error) {
@@ -1043,7 +1052,6 @@ func Munmap(b []byte) (err error) {
 // Newfstatat
 // Nfsservctl
 // Personality
-// Poll
 // Ppoll
 // Pselect6
 // Ptrace