bpo-39008: Require Py_ssize_t for PySys_Audit formats rather than raise a deprecation warning (GH-17540)

(cherry picked from commit b8cbe74)

Co-authored-by: Steve Dower <steve.dower@python.org>

Author: miss-islington

Doc/c-api/sys.rst

@@ -320,10 +320,18 @@ accessible to C code.  They all work with the current interpreter thread's
    arguments to this function will be consumed, using it may cause reference
    leaks.)
 
+   Note that ``#`` format characters should always be treated as
+   ``Py_ssize_t``, regardless of whether ``PY_SSIZE_T_CLEAN`` was defined.
+
    :func:`sys.audit` performs the same function from Python code.
 
    .. versionadded:: 3.8
 
+   .. versionchanged:: 3.8.2
+
+      Require ``Py_ssize_t`` for ``#`` format characters. Previously, an
+      unavoidable deprecation warning was raised.
+
 
 .. c:function:: int PySys_AddAuditHook(Py_AuditHookFunction hook, void *userData)
 

Misc/NEWS.d/next/Core and Builtins/2019-12-09-10-38-51.bpo-39008.Rrp6f1.rst

@@ -0,0 +1,3 @@
+:c:func:`PySys_Audit` now requires ``Py_ssize_t`` to be used for size
+arguments in the format string, regardless of whethen ``PY_SSIZE_T_CLEAN``
+was defined at include time.

Python/sysmodule.c

@@ -159,7 +159,7 @@ PySys_Audit(const char *event, const char *argFormat, ...)
     if (argFormat && argFormat[0]) {
         va_list args;
         va_start(args, argFormat);
-        eventArgs = Py_VaBuildValue(argFormat, args);
+        eventArgs = _Py_VaBuildValue_SizeT(argFormat, args);
         va_end(args);
         if (eventArgs && !PyTuple_Check(eventArgs)) {
             PyObject *argTuple = PyTuple_Pack(1, eventArgs);