Prevent greenlet from building on free-threaded Python

[jamadden]

We don't set the flag that indicates we're compatible with free-threading, so loading us would automatically enable the GIL according to the Python documentation. It is thus misleading that we can even build on a free-threaded Python and get the "t" suffix, e.g., "313t".

The make-manylinux script has some support for skipping free-threaded Python's, but it's neither complete nor sufficient.

The trouble is that CPython doesn't document a way to detect at compile time that it is built on free-threading. At least, not that I could see in the "Porting to 3.13" and "C API Changes" sections of the release notes.

[LeroyK111]

0.06s - pydevd: GEVENT_SUPPORT is set but gevent is not available in the environment. Please unset GEVENT_SUPPORT from the environment variables or install gevent. Traceback (most recent call last): File "c:\Users\Administrator\.vscode\extensions\ms-python.debugpy-2024.13.2024101501-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py", line 166, in <module> from _pydevd_bundle import pydevd_gevent_integration File "c:\Users\Administrator\.vscode\extensions\ms-python.debugpy-2024.13.2024101501-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_gevent_integration.py", line 2, in <module> import greenlet File "d:\python\Lib\site-packages\greenlet\__init__.py", line 29, in <module> from ._greenlet import _C_API # pylint:disable=no-name-in-module ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ModuleNotFoundError: No module named 'greenlet._greenlet'

So, I configured the launch.json file in VSCode and set the "gevent" field to false. After that, I was able to use Python's free-threaded version, which disables the GIL (Global Interpreter Lock) without any issues.

[jamadden]

If you load the extension, it's going to initialize the GIL. If you force Python to not initialize the GIL, the extension will be broken. Do not do this.