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/wscript b/tools/ndnsec/wscript
new file mode 100644
index 0000000..9f61ae4
--- /dev/null
+++ b/tools/ndnsec/wscript
@@ -0,0 +1,14 @@
+# -*- Mode: python; py-indent-offset: 4; indent-tabs-mode: nil; coding: utf-8; -*-
+
+top = '../../'
+
+def build(bld):
+    bld.objects(target='tool-ndnsec-objects',
+                source=bld.path.ant_glob('*.cpp', excl=['main.cpp']),
+                features='pch',
+                headers='ndnsec-pch.hpp',
+                use='ndn-cxx')
+    bld.program(name='tool-ndnsec',
+                target=top + 'bin/ndnsec',
+                source=['main.cpp'],
+                use='tool-ndnsec-objects')