build: pass pkg_config_path to check_cfg() when looking for libndn-cxx

Instead of modifying os.environ

Refs: #5042
Change-Id: If6ac10e5f83a48fa85d9b1dec1a2ae1a59d686ac
diff --git a/PSync.pc.in b/PSync.pc.in
index e72112c..711e4ba 100644
--- a/PSync.pc.in
+++ b/PSync.pc.in
@@ -3,8 +3,7 @@
 includedir=@INCLUDEDIR@
 
 Name: PSync
-Description: PSync library
+Description: NDN PSync library
 Version: @VERSION@
 Libs: -L${libdir} -lPSync
 Cflags: -I${includedir}
-