Skip the SigWait requeue test where pcntl has no sigwaitinfo()

macOS has no sigwaitinfo(), so the test died on an undefined function; it
skips like the other signal-op tests.

Author: bukka

ext/standard/tests/streams/hooks/ring-sigwait-requeue.phpt

@@ -6,6 +6,7 @@ posix
 --SKIPIF--
 <?php
 if (!class_exists(Io\Ring\Engine::class)) die("skip Io\\Ring\\Engine not available");
+if (!function_exists('pcntl_sigwaitinfo')) die('skip pcntl_sigwaitinfo() not available');
 ?>
 --FILE--
 <?php