nghttp: Fix compile error and warning with libc++

src/nghttp.cc

@@ -1057,6 +1057,7 @@ struct HttpClient {
       auto& req_stat = req->stat;
       auto request_time = (i == 0) ? stat.started_system_time :
         stat.started_system_time +
+        std::chrono::duration_cast<std::chrono::system_clock::duration>
         (req_stat.on_request_time - stat.on_started_time);
 
       auto wait_delta = std::chrono::duration_cast

src/util.cc

@@ -729,7 +729,8 @@ std::string format_iso8601(const std::chrono::system_clock::time_point& tp)
   char buf[128];
 
   auto nwrite = strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%S", &tms);
-  snprintf(&buf[nwrite], sizeof(buf) - nwrite, ".%03ldZ", t.count() % 1000);
+  snprintf(&buf[nwrite], sizeof(buf) - nwrite, ".%03dZ",
+           static_cast<int>(t.count() % 1000));
 
   return buf;
 }