build: add PCHs for ndnsec and unit tests, fine-tune the existing ones

A full debug+tests build now takes 10% less time with gcc-9 and 21% less
with clang-10. Release builds (without tests) are only marginally faster
with gcc and 7% faster with clang.

Change-Id: I494778fe44cecc6209819a49f48a03f4d16c36af
diff --git a/tools/ndnsec/main.cpp b/tools/ndnsec/main.cpp
index 8548748..c0be01b 100644
--- a/tools/ndnsec/main.cpp
+++ b/tools/ndnsec/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2019 Regents of the University of California.
+ * Copyright (c) 2013-2020 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -20,12 +20,12 @@
  */
 
 #include "ndnsec.hpp"
-#include "util.hpp"
 
 #include "ndn-cxx/util/logger.hpp"
 #include "ndn-cxx/version.hpp"
 
 #include <boost/exception/diagnostic_information.hpp>
+#include <iostream>
 
 NDN_LOG_INIT(ndnsec);