Once upon a time XPIDL_MODULE and MODULE were kind of the same and
MODULE got mass-converted into XPIDL_MODULE with the removal of MODULE
in bug 939044. Unfortunately, we forgot to add a check for XPIDL_MODULE
being defined if XPIDL_SOURCES isn't (a build config that makes no sense
and only results in cargo culting).
This patch corrects that oversight.
--HG--
extra : rebase_source : d609e2baa8d16df97c944bc9def26ad05527d937
