* ext/extmk.rb (extmake): Use Logging.open to switch stdout and
  stderr.  Delay Logging::log_close until the failure message is
  written.  Write the failure message only if log file is opened.

* lib/mkmf.rb (Logging.log_opened?): New method.

  [ruby-dev:47215] [Bug #8209]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40080 b2dd03c8-39d4-4d8f-98ff-823fe69b080e