Add -Wextra-semi -Wundefined-func-template to the default CXXFLAGS

And fix the resulting compilation errors.

Change-Id: I16f679836a0cf2a3ff5dfcf6f6b67bfbfe4cdbd7
Refs: #4248
diff --git a/src/mgmt/nfd/strategy-choice.hpp b/src/mgmt/nfd/strategy-choice.hpp
index ba840f0..55871bb 100644
--- a/src/mgmt/nfd/strategy-choice.hpp
+++ b/src/mgmt/nfd/strategy-choice.hpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -87,6 +87,8 @@
   mutable Block m_wire;
 };
 
+NDN_CXX_DECLARE_WIRE_ENCODE_INSTANTIATIONS(StrategyChoice);
+
 bool
 operator==(const StrategyChoice& a, const StrategyChoice& b);