eval.c: suppress a warning

* eval.c (setup_exception): suppress a maybe-uninitialized false
  warning by gcc 4.8.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46566 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-06-27

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46567 b2dd03c8-39d4-4d8f-98ff-823fe69b080e