mkmf/base.rb: clean up tmpdir
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49835 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf/base.rb: clean up tmpdir
clean up temporary directory.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49835 b2dd03c8-39d4-4d8f-98ff-823fe69b080e