For the current cases, a few string substitions is enough to
make dtrace(1) scripts work with stap(1).  For more complex
scripts (maybe in the future), we may pass a hash with
implementation-specific scripts.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63581 b2dd03c8-39d4-4d8f-98ff-823fe69b080e