subrepo: use separate instances of empty lists in status

We do modify the lists that make up the status in several places, so
it seems risky to use the same instance of a list for several
different status types. Use a separate empty list for each type
instead.

mercurial/subrepo.py

@@ -1582,7 +1582,7 b' class gitsubrepo(abstractsubrepo):'
             elif status == 'D':
                 removed.append(f)
 
-        deleted = unknown = ignored = clean = []
+        deleted, unknown, ignored, clean = [], [], [], []
         return scmutil.status(modified, added, removed, deleted,
                               unknown, ignored, clean)