eval_intern.h: jmpbuf must be accessible

* eval_intern.h (TH_PUSH_TAG): ensure jmpbuf to be accessible before
  pushing tag to get rid of unaccessible tag by stack overflow.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40791 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-05-17

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40792 b2dd03c8-39d4-4d8f-98ff-823fe69b080e