bpo-39825: fix sysconfig.get_config_var('EXT_SUFFIX') on windows

[mattip]

Fixes sysconfig.get_config_var('EXT_SUFFIX') to the expected full platform_tag.extension format.

May influence downstream packages like wheel (@agronholm) which use this value,

https://bugs.python.org/issue39825

[mattip]

@agronholm @pitrou: any thoughts?

[pitrou]

This looks fine to me. @zooba Any opinions?

[agronholm]

Wheel does not seem to use this anyway.

[pitrou]

@pfmoore Would you like to opine on this?

[mattip]

ping. Does this warrant a news item?

[zooba]

Looks fine to me, and yeah, let's give it a NEWS item (the NEWS should be the first place people search for "why did my thing just break", so try and describe it in terms that attract the sort of query).

Also, my GitHub notifications are an overflowing bottomless pit. Ping me on bpo to get my attention.

[mattip]

NEWS fragment added. Since @zooba has no objections, could another core dev finish this off?

[miss-islington]

Thanks @mattip for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.8, 3.9.
🐍🍒⛏🤖

[zooba]

Thanks!

[bedevere-bot]

GH-23681 is a backport of this pull request to the 3.9 branch.

[bedevere-bot]

GH-23682 is a backport of this pull request to the 3.8 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Shared 3.x has failed when building commit c0afb7f.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/483/builds/513) and take a look at the build logs.
4. Check if the failure is related to this commit (c0afb7f) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/483/builds/513

Failed tests:

• test_sysconfig

Failed subtests:

• test_EXT_SUFFIX_in_vars - test.test_sysconfig.TestSysConfig

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

405 tests OK.

10 slowest tests:

• test_smtpnet: 6 min 8 sec
• test_nntplib: 3 min 49 sec
• test_concurrent_futures: 3 min 36 sec
• test_tokenize: 2 min 14 sec
• test_multiprocessing_spawn: 2 min 8 sec
• test_urllib2: 2 min 1 sec
• test_unparse: 2 min
• test_multiprocessing_forkserver: 1 min 46 sec
• test_subprocess: 1 min 30 sec
• test_asyncio: 1 min 14 sec

1 test failed:
test_sysconfig

19 tests skipped:
test_dbm_gnu test_devpoll test_epoll test_idle test_ioctl
test_msilib test_ossaudiodev test_spwd test_startfile test_tcl
test_tix test_tk test_ttk_guionly test_ttk_textonly test_turtle
test_winconsoleio test_winreg test_winsound test_zipfile64

1 re-run test:
test_sysconfig

Total duration: 13 min 50 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-564d/build/Lib/test/test_sysconfig.py", line 368, in test_EXT_SUFFIX_in_vars
    self.assertEqual(vars['EXT_SUFFIX'], _imp.extension_suffixes()[0])
AssertionError: '.so' != '.cpython-310d.so'
- .so
+ .cpython-310d.so

[mattip]

Did I miss something? The FREEBSD buildbot is failing with

======================================================================
FAIL: test_EXT_SUFFIX_in_vars (test.test_sysconfig.TestSysConfig)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-564d/build/Lib/test/test_sysconfig.py", line 368, in test_EXT_SUFFIX_in_vars
    self.assertEqual(vars['EXT_SUFFIX'], _imp.extension_suffixes()[0])
AssertionError: '.so' != '.cpython-310d.so'
- .so
+ .cpython-310d.so