[issue40060] socket.TCP_NOTSENT_LOWAT is missing in official macOS builds

[Ma Lin]

Ma Lin <malincns at 163.com> added the comment:

Windows build encountered a similar problem, see issue32394.
The solution is to check the runtime system version when importing socket module, if it is an older system, delete the constants. [1]

issue32394 has a small script (winsdk_watchdog.py) to help find such constants, usage:
1, build a CPython build with old SDK.
2, use winsdk_watchdog.py, dump possible affected constants to a file `winsdk_dump.json`.
3, build a CPython build with new SDK.
4, use winsdk_watchdog.py, compare constants between two builds .

If a new constant is introduced by new SDK/API, we remove it on older system during runtime.
Otherwise we can ignore this new constant, this means it has nothing to do with the new SDK.
(msg311858 is a demo.)

We don't need to use winsdk_watchdog.py routinely, just use it when updating the building SDK, this process only takes about 10~20 minutes.

I think macOS build can also uses this process.

[1]
The commit:
https://github.com/python/cpython/commit/19e7d48ce89422091f9af93038b9fee075d46e9e

Note that there was a minor fix later:
https://github.com/python/cpython/commit/8905fcc85a6fc3ac394bc89b0bbf40897e9497a#diff-a47fd74731aeb547ad780900bb8e6953

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nosy: +Ma Lin

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<https://bugs.python.org/issue40060>
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