eval.c: refactor exception cause

* eval.c (setup_exception): set up cause after exception to be raised
  is fixed.  [Feature #8257]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43684 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_exception.rb

@@ -479,16 +479,31 @@ end.join
 
   def test_cause
     msg = "[Feature #8257]"
+    cause = nil
     e = assert_raise(StandardError) {
       begin
         raise msg
       rescue => e
-        assert_nil(e.cause, msg)
+        cause = e.cause
         raise StandardError
       end
     }
+    assert_nil(cause, msg)
     cause = e.cause
     assert_instance_of(RuntimeError, cause, msg)
     assert_equal(msg, cause.message, msg)
   end
+
+  def test_cause_reraised
+    msg = "[Feature #8257]"
+    cause = nil
+    e = assert_raise(RuntimeError) {
+      begin
+        raise msg
+      rescue => e
+        raise e
+      end
+    }
+    assert_not_same(e, e.cause, "#{msg}: should not be recursive")
+  end
 end