When available, use async_signals in Phabricator

Summary: Ref T9640. See D17200 for the analogous change in libphutil.

Test Plan: See D17200.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9640

Differential Revision: https://secure.phabricator.com/D17201

scripts/daemon/launch_daemon.php

@@ -5,7 +5,11 @@
 // script, except it loads the Phabricator environment and adds some Phabricator
 // specific flags.
 
-declare(ticks = 1);
+if (function_exists('pcntl_async_signals')) {
+  pcntl_async_signals(true);
+} else {
+  declare(ticks = 1);
+}
 
 $root = dirname(dirname(dirname(__FILE__)));
 require_once $root.'/scripts/__init_script__.php';