bpo-33012: Fix invalid function cast warnings with gcc 8 for METH_NOARGS. (GH-6030)

METH_NOARGS functions need only a single argument but they are cast
into a PyCFunction, which takes two arguments.  This triggers an
invalid function cast warning in gcc8 due to the argument mismatch.
Fix this by adding a dummy unused argument.

Modules/_collectionsmodule.c

@@ -512,7 +512,7 @@ deque_inplace_concat(dequeobject *deque, PyObject *other)
 }
 
 static PyObject *
-deque_copy(PyObject *deque)
+deque_copy(PyObject *deque, PyObject *Py_UNUSED(ignored))
 {
     dequeobject *old_deque = (dequeobject *)deque;
     if (Py_TYPE(deque) == &deque_type) {
@@ -563,7 +563,7 @@ deque_concat(dequeobject *deque, PyObject *other)
         return NULL;
     }
 
-    new_deque = deque_copy((PyObject *)deque);
+    new_deque = deque_copy((PyObject *)deque, NULL);
     if (new_deque == NULL)
         return NULL;
     result = deque_extend((dequeobject *)new_deque, other);
@@ -659,7 +659,7 @@ deque_clear(dequeobject *deque)
 }
 
 static PyObject *
-deque_clearmethod(dequeobject *deque)
+deque_clearmethod(dequeobject *deque, PyObject *Py_UNUSED(ignored))
 {
     deque_clear(deque);
     Py_RETURN_NONE;
@@ -754,7 +754,7 @@ deque_repeat(dequeobject *deque, Py_ssize_t n)
     dequeobject *new_deque;
     PyObject *rv;
 
-    new_deque = (dequeobject *)deque_copy((PyObject *) deque);
+    new_deque = (dequeobject *)deque_copy((PyObject *) deque, NULL);
     if (new_deque == NULL)
         return NULL;
     rv = deque_inplace_repeat(new_deque, n);
@@ -1576,7 +1576,7 @@ static PyNumberMethods deque_as_number = {
  };
 
 static PyObject *deque_iter(dequeobject *deque);
-static PyObject *deque_reviter(dequeobject *deque);
+static PyObject *deque_reviter(dequeobject *deque, PyObject *Py_UNUSED(ignored));
 PyDoc_STRVAR(reversed_doc,
     "D.__reversed__() -- return a reverse iterator over the deque");
 
@@ -1587,9 +1587,9 @@ static PyMethodDef deque_methods[] = {
         METH_O,                  appendleft_doc},
     {"clear",                   (PyCFunction)deque_clearmethod,
         METH_NOARGS,             clear_doc},
-    {"__copy__",                (PyCFunction)deque_copy,
+    {"__copy__",                deque_copy,
         METH_NOARGS,             copy_doc},
-    {"copy",                    (PyCFunction)deque_copy,
+    {"copy",                    deque_copy,
         METH_NOARGS,             copy_doc},
     {"count",                   (PyCFunction)deque_count,
         METH_O,                  count_doc},
@@ -1774,7 +1774,7 @@ dequeiter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 }
 
 static PyObject *
-dequeiter_len(dequeiterobject *it)
+dequeiter_len(dequeiterobject *it, PyObject *Py_UNUSED(ignored))
 {
     return PyLong_FromSsize_t(it->counter);
 }
@@ -1782,7 +1782,7 @@ dequeiter_len(dequeiterobject *it)
 PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it)).");
 
 static PyObject *
-dequeiter_reduce(dequeiterobject *it)
+dequeiter_reduce(dequeiterobject *it, PyObject *Py_UNUSED(ignored))
 {
     return Py_BuildValue("O(On)", Py_TYPE(it), it->deque, Py_SIZE(it->deque) - it->counter);
 }
@@ -1841,7 +1841,7 @@ static PyTypeObject dequeiter_type = {
 static PyTypeObject dequereviter_type;
 
 static PyObject *
-deque_reviter(dequeobject *deque)
+deque_reviter(dequeobject *deque, PyObject *Py_UNUSED(ignored))
 {
     dequeiterobject *it;
 
@@ -1896,7 +1896,7 @@ dequereviter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         return NULL;
     assert(type == &dequereviter_type);
 
-    it = (dequeiterobject*)deque_reviter((dequeobject *)deque);
+    it = (dequeiterobject*)deque_reviter((dequeobject *)deque, NULL);
     if (!it)
         return NULL;
     /* consume items from the queue */
@@ -2001,7 +2001,7 @@ defdict_missing(defdictobject *dd, PyObject *key)
 PyDoc_STRVAR(defdict_copy_doc, "D.copy() -> a shallow copy of D.");
 
 static PyObject *
-defdict_copy(defdictobject *dd)
+defdict_copy(defdictobject *dd, PyObject *Py_UNUSED(ignored))
 {
     /* This calls the object's class.  That only works for subclasses
        whose class constructor has the same signature.  Subclasses that
@@ -2015,7 +2015,7 @@ defdict_copy(defdictobject *dd)
 }
 
 static PyObject *
-defdict_reduce(defdictobject *dd)
+defdict_reduce(defdictobject *dd, PyObject *Py_UNUSED(ignored))
 {
     /* __reduce__ must return a 5-tuple as follows: