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/floatobject.c b/Objects/floatobject.c
index 67f9e5d..8d83f00 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -124,7 +124,7 @@
             return PyErr_NoMemory();
     }
     /* Inline PyObject_New */
-    (void)PyObject_INIT(op, &PyFloat_Type);
+    (void)PyObject_INIT((PyObject *)op, &PyFloat_Type);
     op->ob_fval = fval;
     return (PyObject *) op;
 }