bpo-35059: Convert PyObject_INIT() to function (GH-10077)

* Convert PyObject_INIT() and PyObject_INIT_VAR() macros to static
  inline functions.
* Fix usage of these functions: cast to PyObject* or PyVarObject*.
diff --git a/Objects/methodobject.c b/Objects/methodobject.c
index 5ad2831..9176e39 100644
--- a/Objects/methodobject.c
+++ b/Objects/methodobject.c
@@ -31,7 +31,7 @@
     op = free_list;
     if (op != NULL) {
         free_list = (PyCFunctionObject *)(op->m_self);
-        (void)PyObject_INIT(op, &PyCFunction_Type);
+        (void)PyObject_INIT((PyObject *)op, &PyCFunction_Type);
         numfree--;
     }
     else {