files need timestamps to be kept are only ar-archive on a few
  platforms, and be installed by instruby.rb but not INSTALL.
  fixed: [ruby-core:04721]

* mkconfig.rb: purge autoconf value variables.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@8338 b2dd03c8-39d4-4d8f-98ff-823fe69b080e