build: Fix build when std::to_string is not available

Change-Id: If34fcebe17bd7e3de23655680957fa6e0df27676
Refs: #4393
diff --git a/tests/other/fw/congestion-mark-strategy.cpp b/tests/other/fw/congestion-mark-strategy.cpp
index ea73d4e..3e2ccce 100644
--- a/tests/other/fw/congestion-mark-strategy.cpp
+++ b/tests/other/fw/congestion-mark-strategy.cpp
@@ -62,7 +62,7 @@
 
   if (parsed.version && *parsed.version != getStrategyName()[-1].toVersion()) {
     BOOST_THROW_EXCEPTION(std::invalid_argument(
-      "CongestionMarkStrategy does not support version " + std::to_string(*parsed.version)));
+      "CongestionMarkStrategy does not support version " + to_string(*parsed.version)));
   }
   this->setInstanceName(makeInstanceName(name, getStrategyName()));
 }
diff --git a/tests/tools/nfdc/rib-module.t.cpp b/tests/tools/nfdc/rib-module.t.cpp
index be9fcfb..0b28e9b 100644
--- a/tests/tools/nfdc/rib-module.t.cpp
+++ b/tests/tools/nfdc/rib-module.t.cpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2014-2017,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
@@ -391,7 +391,7 @@
     cmd.validateRequest(req);
     cmd.applyDefaultsToRequest(req);
     BOOST_CHECK_EQUAL(req.getName(), "/nm5y8X8b2");
-    BOOST_CHECK_MESSAGE(faceIds.erase(req.getFaceId()), "expected face " + std::to_string(req.getFaceId()));
+    BOOST_CHECK_MESSAGE(faceIds.erase(req.getFaceId()), "expected face " + to_string(req.getFaceId()));
     BOOST_CHECK_EQUAL(req.getOrigin(), ndn::nfd::ROUTE_ORIGIN_STATIC);
 
     this->succeedCommand(interest, req);