Revision 318031

MFC r317888 and two upstream prerequisites:

Pull in r227097 from upstream libc++ trunk (by Marshall Clow):

  Fix PR21428. Buffer was one byte too small in octal formatting case.
  Add test

Pull in r268009 from upstream libc++ trunk (by Eric Fiselier):

  Fix PR21428 for long. Buffer was one byte too small in octal
  formatting case. Rename previously added test

Pull in r302362 from upstream libc++ trunk (by me):

  Ensure showbase does not overflow do_put buffers

  Summary:
  In https://bugs.freebsd.org/207918, Daniel McRobb describes how using
  std::showbase with ostreams can cause truncation of unsigned long long
  when output format is octal.  In fact, this can even happen with
  unsigned int and unsigned long.

  To ensure this does not happen, add one additional character to the
  do_put buffers if std::showbase is on.  Also add a test case.

  Reviewers: EricWF, mclow.lists

  Reviewed By: EricWF

  Subscribers: cfe-commits, emaste

  Differential Revision: https://reviews.llvm.org/D32670

PR:		207918