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/key-locator.cpp b/src/key-locator.cpp
index 8eef8cc..50453d9 100644
--- a/src/key-locator.cpp
+++ b/src/key-locator.cpp
@@ -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).
@@ -74,11 +74,7 @@
   return totalLength;
 }
 
-template size_t
-KeyLocator::wireEncode<encoding::EncoderTag>(EncodingImpl<encoding::EncoderTag>& encoder) const;
-
-template size_t
-KeyLocator::wireEncode<encoding::EstimatorTag>(EncodingImpl<encoding::EstimatorTag>& encoder) const;
+NDN_CXX_DEFINE_WIRE_ENCODE_INSTANTIATIONS(KeyLocator);
 
 const Block&
 KeyLocator::wireEncode() const