Revision 318032

MFC r317888:

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