Windows debug abi3t extensions autolink python316_d.lib instead of python316t_d.lib

Bắt đầu với phần chọn autolink trong PC/pyconfig.h và phần suy ra ABI trong Include/pyabi.h. Tái hiện probe được ghi lại trong tài liệu hoặc kiểm tra PR được liên kết gh-157623, sau đó xác minh rằng trường hợp abi3t debug trên Windows phát ra chỉ thị thư viện import free-threaded mà không yêu cầu Py_GIL_DISABLED tường minh.

Bug report

Bug description:

On the current main branch, an MSVC-compatible debug extension that defines
Py_LIMITED_API and Py_TARGET_ABI3T can select the ordinary debug import
library instead of the free-threaded debug library.

The ordering in the public headers appears to cause the mismatch:

1. PC/pyconfig.h selects the autolink library.
2. Only later does Include/pyabi.h derive Py_GIL_DISABLED from
   Py_TARGET_ABI3T.

The debug autolink branch in PC/pyconfig.h currently checks only
Py_GIL_DISABLED. An abi3t extension identifies its target with
Py_TARGET_ABI3T, so it does not necessarily define Py_GIL_DISABLED before
including these headers.

I reproduced this by compiling a minimal Windows x86-64 COFF object with Clang
in MSVC-compatible target mode. The probe defines _DEBUG, Py_LIMITED_API,
and Py_TARGET_ABI3T=0x030f0000, then includes the two headers in their normal
order:

#include "PC/pyconfig.h"
#include "Include/pyabi.h"

#ifndef Py_GIL_DISABLED
#  error "Py_TARGET_ABI3T did not enable Py_GIL_DISABLED"
#endif

int cpython_abi3t_autolink_probe;

The resulting object's .drectve section contains:

/DEFAULTLIB:python316_d.lib

Defining Py_GIL_DISABLED explicitly before including the headers instead
produces:

/DEFAULTLIB:python316t_d.lib

The release abi3t case already selects python3t.lib; the mismatch is specific
to the versioned debug-library branch. The PCbuild naming also identifies
python316t_d.lib as the free-threaded debug import library.

A minimal possible fix is to recognize the ABI target at the point where the
autolink library is selected:

-#if defined(Py_GIL_DISABLED)
+#if defined(Py_GIL_DISABLED) || defined(Py_TARGET_ABI3T)

With that change, the original probe, without an explicit
Py_GIL_DISABLED, emits /DEFAULTLIB:python316t_d.lib.

This test inspects the Windows linker directive emitted by the public headers,
but I have not run a native Windows extension build. Could you confirm whether
Py_TARGET_ABI3T should select the free-threaded debug import library at this
earlier point? If so, I can prepare a pull request with this change, or adjust
it if changing the include/derivation order is preferred.

CPython versions tested on

CPython main.

Operating systems tested on

The reproducer was cross-compiled on Linux for the Windows x86-64 MSVC target.
Native Windows validation has not yet been performed -- as I do not have a windows machine.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-157623