Test for pcntl availability from the command line, not Apache

Summary:
In RHEL6 at the least, pcntl installs from distro package management to the CLI
but not to Apache. Since we don't need it in apache and it's a pain to build
manually, just verify it exists on the CLI.

Test Plan:
Simulated script failures and verified setup output.

Reviewed By: codeblock
Reviewers: codeblock, aran, jungejason, tuomaspelkonen
CC: aran, epriestley, kevinwallace, codeblock
Differential Revision: 380

scripts/setup/pcntl_available.php

@@ -0,0 +1,24 @@
+#!/usr/bin/env php
+<?php
+
+/*
+ * Copyright 2011 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+if (extension_loaded('pcntl')) {
+  echo "YES\n";
+} else {
+  echo "NO\n";
+}