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/cert-gen.cpp b/tools/ndnsec/cert-gen.cpp
index ec630c9..1749b2b 100644
--- a/tools/ndnsec/cert-gen.cpp
+++ b/tools/ndnsec/cert-gen.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).
  *
@@ -26,6 +26,7 @@
 #include "ndn-cxx/security/transform/buffer-source.hpp"
 #include "ndn-cxx/security/transform/public-key.hpp"
 #include "ndn-cxx/security/transform/stream-sink.hpp"
+#include "ndn-cxx/security/v2/additional-description.hpp"
 
 namespace ndn {
 namespace ndnsec {