[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/example.h

@@ -0,0 +1,9 @@
+extern char *s;
+extern int x;
+
+class Sync {
+	public:
+		int x;
+		char *s;
+		void printer(void);
+};