Code freeze for 2.20 approaching

[Roland McGrath]

I added two items to desirable:
* -Wundef clean (I would prefer that this be a blocker, but that needs
  buy-in from people committing to finish the cleanup)
* NPTL no longer add-in.  I might well have this done by the end of the
  month.  I won't recommend it be a blocker because I don't want people to
  be stuck waiting for me, but I think if by the end of the month it looks
  pretty close then we should slip the freeze to finish it.


Thanks,
Roland