[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/test-suite/php5/using1_runme.php

@@ -0,0 +1,9 @@
+<?php
+
+require "tests.php";
+require "using1.php";
+if (! class_exists("_fooimpl")) die("_fooimpl class not found\n");
+if (! 3==spam(3)) die("spam function not working right\n");
+
+check::done();
+?>