Adjust PHP sync example

Make it work with how globals are actually wrapped.  It looks like
this example has never been right, but nobody noticed before PHP 8
started warning about the use of unset variables.

This reveals that handling of std::string properties needs fixing.

Examples/php/sync/example.h

@@ -1,9 +1,14 @@
-extern char *s;
+#include <string>
+
+extern std::string s;
 extern int x;
 
 class Sync {
 	public:
 		int x;
-		char *s;
-		void printer(void);
+		std::string s;
+		void printer();
+		void all_change();
+
+		Sync() : x(0) { }
 };