config: read system hgrc in lexicographical order

This is similar to edbcf5b239f9 (config: read configs from directories
in lexicographical order, 2019-04-03). Apparently I forgot to sort the
system hgrc files there. That's fixed by this patch.

Differential Revision: https://phab.mercurial-scm.org/D9269

mercurial/scmposix.py

@@ -27,7 +27,7 b' def _rcfiles(path):'
         rcs.extend(
             [
                 os.path.join(rcdir, f)
-                for f, kind in util.listdir(rcdir)
+                for f, kind in sorted(util.listdir(rcdir))
                 if f.endswith(b".rc")
             ]
         )

mercurial/scmwindows.py

@@ -31,7 +31,7 b' def systemrcpath():'
 
     def _processdir(progrcd):
         if os.path.isdir(progrcd):
-            for f, kind in util.listdir(progrcd):
+            for f, kind in sorted(util.listdir(progrcd)):
                 if f.endswith(b'.rc'):
                     rcpath.append(os.path.join(progrcd, f))