Python 3.11 loses the ability to set PYTHON_DECIMAL_WITH_MACHINE

Bug report

Python 3.10 had the ability to set PYTHON_DECIMAL_WITH_MACHINE to override the choice of configuration for the _decimal module:
https://github.com/python/cpython/blob/dcb342b5f9d931b030ca310bf3e175bbc54df5aa/setup.py#L2388-L2397

Since Python 3.11, this is no longer possible. This feature was necessary, on macOS particularly, with the --with-system-libmpdec option if that system libmpdec is configured differently to the default Python config. On macOS, the default Python config forces universal, while setting PYTHON_DECIMAL_WITH_MACHINE allowed it to be single-arch.

libmpdec produces different headers depending on how it was built, which is why the setting is important to be able to override. Without it, the _decimal module will fail to compile if the default does not match how system libmpdec was built.

Homebrew's Python currently depends on this feature.

A test within CPython also seems to depend on this feature: https://github.com/python/cpython/blob/f4c03484da59049eb62a9bf7777b963e2267d187/Modules/_decimal/tests/runall-memorydebugger.sh#L63-L79

Your environment

• CPython versions tested on: 3.11.0rc2
• Operating system and architecture: macOS 12 (x86_64 and arm64)

レポートにリンクされている Python 3.10 の setup.py の行を、_decimal の現在のビルドロジックと比較し、その後 Modules/_decimal/tests/runall-memorydebugger.sh でその設定がどのように使用されているかを確認します。報告された macOS アーキテクチャで --with-system-libmpdec を使った override が機能し、関連するビルドおよびテストのチェックが成功することを確認します。