[1924] Return missing pythondir

It was moved to other makefile by accident while it should have been
moved.

src/lib/python/isc/cc/Makefile.am

@@ -3,6 +3,8 @@ SUBDIRS = . cc_generated tests
 python_PYTHON =	__init__.py data.py session.py message.py
 EXTRA_DIST = proto_defs.py
 
+pythondir = $(pyexecdir)/isc/cc
+
 CLEANDIRS = __pycache__
 
 clean-local: