* vm_eval.c (rb_catch_obj): add volatile to tag to prevent crash
  experimentally.
  http://www.rubyist.net/~akr/chkbuild/debian/ruby-trunk/log/20130515T133500Z.log.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40785 b2dd03c8-39d4-4d8f-98ff-823fe69b080e