build: Embed setting of PKG_CONFIG_PATH variable to commonly used values

Change-Id: I8f70e1bedad13f77bbd40ab53d2e31717836a667
Refs: #2178
diff --git a/wscript b/wscript
index d2aff10..548fad3 100644
--- a/wscript
+++ b/wscript
@@ -63,6 +63,10 @@
 
     conf.find_program('bash', var='BASH')
 
+    if not os.environ.has_key('PKG_CONFIG_PATH'):
+        os.environ['PKG_CONFIG_PATH'] = ':'.join([
+            '/usr/local/lib/pkgconfig',
+            '/opt/local/lib/pkgconfig'])
     conf.check_cfg(package='libndn-cxx', args=['--cflags', '--libs'],
                    uselib_store='NDN_CXX', mandatory=True)