Set custom PKG_CONFIG_PATH if unset

Closes https://github.com/named-data/ndn-traffic-generator/pull/8

Change-Id: I3201688dda24c38b99d3bfea34ba70f42da1e41c

wscript

@@ -1,14 +1,22 @@
 # -*- Mode: python; py-indent-offset: 4; indent-tabs-mode: nil; coding: utf-8; -*-
-VERSION='0.1'
-APPNAME="ndn-traffic-generator"
+
+VERSION = '0.1'
+APPNAME = 'ndn-traffic-generator'
+
+from waflib import Utils
+import os
 
 def options(opt):
     opt.load(['compiler_cxx', 'gnu_dirs'])
-    opt.load(['default-compiler-flags'], tooldir=['.waf-tools'])
+    opt.load(['default-compiler-flags'],
+             tooldir=['.waf-tools'])
 
 def configure(conf):
     conf.load(['compiler_cxx', 'gnu_dirs',
                'default-compiler-flags'])
+
+    if 'PKG_CONFIG_PATH' not in os.environ:
+        os.environ['PKG_CONFIG_PATH'] = Utils.subst_vars('${LIBDIR}/pkgconfig', conf.env)
     conf.check_cfg(package='libndn-cxx', args=['--cflags', '--libs'],
                    uselib_store='NDN_CXX', mandatory=True)