pythongh-111178: fix UBSan failures in Modules/_winapi.c (pythonGH-129796)

Fix UBSan failures for `OverlappedObject`

Suppress unused return values

Author: picnixz

Modules/_winapi.c

@@ -144,25 +144,29 @@ typedef struct {
     Py_buffer write_buffer;
 } OverlappedObject;
 
+#define OverlappedObject_CAST(op)   ((OverlappedObject *)(op))
+
 /*
 Note: tp_clear (overlapped_clear) is not implemented because it
 requires cancelling the IO operation if it's pending and the cancellation is
 quite complex and can fail (see: overlapped_dealloc).
 */
 static int
-overlapped_traverse(OverlappedObject *self, visitproc visit, void *arg)
+overlapped_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    OverlappedObject *self = OverlappedObject_CAST(op);
     Py_VISIT(self->read_buffer);
     Py_VISIT(self->write_buffer.obj);
     Py_VISIT(Py_TYPE(self));
     return 0;
 }
 
 static void
-overlapped_dealloc(OverlappedObject *self)
+overlapped_dealloc(PyObject *op)
 {
     DWORD bytes;
     int err = GetLastError();
+    OverlappedObject *self = OverlappedObject_CAST(op);
 
     PyObject_GC_UnTrack(self);
     if (self->pending) {
@@ -3215,7 +3219,7 @@ winapi_clear(PyObject *module)
 static void
 winapi_free(void *module)
 {
-    winapi_clear((PyObject *)module);
+    (void)winapi_clear((PyObject *)module);
 }
 
 static struct PyModuleDef winapi_module = {