close #4834 add testcase (#16649)

tests/cpp/t4834.nim

@@ -0,0 +1,17 @@
+discard """
+  targets: "cpp"
+"""
+
+# issue #4834
+block:
+  defer:
+    let x = 0
+
+
+proc main() =
+  block:
+    defer:
+      raise newException(Exception, "foo")
+
+doAssertRaises(Exception):
+  main()