download config files

* common.mk (update-config_files): rule to download config files.
* tool/config.guess, tool/config.sub: remove and download from the
  upstream.
* tool/get-config_files: download config files from GNU.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41293 b2dd03c8-39d4-4d8f-98ff-823fe69b080e