eval.c: suppress a warning

* eval.c (setup_exception): suppress a "clobbered" warning by gcc
  4.9.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45183 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

eval.c

@@ -515,7 +515,7 @@ setup_exception(rb_thread_t *th, int tag, volatile VALUE mesg, VALUE cause)
 	PUSH_TAG();
 	if ((status = EXEC_TAG()) == 0) {
 	    th->errinfo = Qnil;
-	    e = rb_obj_as_string(e);
+	    e = rb_obj_as_string(mesg);
 	    th->errinfo = mesg;
 	    if (file && line) {
 		warn_printf("Exception `%"PRIsVALUE"' at %s:%d - %"PRIsVALUE"\n",