common.mk: ifchange for mkconfig.rb
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55338 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
common.mk: ifchange for mkconfig.rb
changed and update the timestamp file.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55338 b2dd03c8-39d4-4d8f-98ff-823fe69b080e