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/complexobject.c b/Objects/complexobject.c
index 6e3d47b..eecdb52 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -228,7 +228,7 @@
     op = (PyComplexObject *) PyObject_MALLOC(sizeof(PyComplexObject));
     if (op == NULL)
         return PyErr_NoMemory();
-    (void)PyObject_INIT(op, &PyComplex_Type);
+    (void)PyObject_INIT((PyObject *)op, &PyComplex_Type);
     op->cval = cval;
     return (PyObject *) op;
 }