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/longobject.c b/Objects/longobject.c
index 6f7fe33..ab5ac34 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -211,7 +211,7 @@
         PyErr_NoMemory();
         return NULL;
     }
-    return (PyLongObject*)PyObject_INIT_VAR(result, &PyLong_Type, size);
+    return (PyLongObject*)PyObject_INIT_VAR((PyVarObject *)result, &PyLong_Type, size);
 }
 
 PyObject *
@@ -5620,7 +5620,7 @@
             assert(v->ob_digit[0] == (digit)abs(ival));
         }
         else {
-            (void)PyObject_INIT(v, &PyLong_Type);
+            (void)PyObject_INIT((PyObject *)v, &PyLong_Type);
         }
         Py_SIZE(v) = size;
         v->ob_digit[0] = (digit)abs(ival);