Fix g++ build for mongoose example

    PUBLISHED_FROM=c581f33e26819d05c9b8484c9dc10c2a3615a34a

examples/simplest_web_server/simplest_web_server.c

@@ -8,7 +8,7 @@ static struct mg_serve_http_opts s_http_server_opts;
 
 static void ev_handler(struct mg_connection *nc, int ev, void *p) {
   if (ev == MG_EV_HTTP_REQUEST) {
-    mg_serve_http(nc, p, s_http_server_opts);
+    mg_serve_http(nc, (struct http_message *) p, s_http_server_opts);
   }
 }