close #13062(add testcase for #13062) (#15956)

tests/ccgbugs/t13062.nim

@@ -0,0 +1,27 @@
+discard """
+  output: "[p = nil]"
+  targets: "c cpp"
+"""
+
+import atomics
+
+type
+  Pledge* {.exportc.} = object
+    p: PledgePtr
+
+  PledgeKind {.exportc.} = enum
+    Single
+    Iteration
+
+  PledgePtr {.exportc.} = ptr object
+    case kind: PledgeKind
+    of Single:
+      impl: PledgeImpl
+    of Iteration:
+      discard
+
+  PledgeImpl {.exportc.} = object
+    fulfilled: Atomic[bool]
+
+var x: Pledge
+echo x.repr