mkmf.rb: use expanded values
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41648 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf.rb: use expanded values
unless extmk. patch by vo.x (Vit Ondruch) at [ruby-core:55653]
[Bug #8115], rhbz#921650.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41648 b2dd03c8-39d4-4d8f-98ff-823fe69b080e