[PHP] Add support for PHP7.

PHP5's C extension API has changed substantially so you need to use
-php7 to specify you want PHP7 compatible wrappers.
Fixes https://github.com/swig/swig/issues/571

Examples/php5/sync/runme.php

@@ -0,0 +1,15 @@
+<?
+
+// Load module and PHP classes.
+include("example.php");
+
+echo "Got new object\n";
+echo "Got string $s and value $x \n";
+
+$s = new Sync();
+echo "Got new object\n";
+
+$s->printer();
+
+?>
+