PEP 757: Make PyLong_DigitArray.obj private (#3966)

peps/pep-0757.rst

@@ -90,9 +90,6 @@ Export API
 Export a Python integer as a digits array::
 
     typedef struct PyLong_DigitArray {
-        // Strong reference to the Python int object.
-        PyObject *obj;
-
         // 1 if the number is negative, 0 otherwise.
         int negative;
 
@@ -101,6 +98,9 @@ Export a Python integer as a digits array::
 
         // Read-only array of unsigned digits.
         const void *digits;
+
+        // Member used internally, must not be used for other purpose.
+        Py_uintptr_t _reserved;
     } PyLong_DigitArray;
 
     PyAPI_FUNC(int) PyLong_AsDigitArray(