gh-158893: Add internal _Py_strerror() function

[vstinner]

Add a new internal _Py_strerror() function to Python/fileutils.c. It uses strerror_r() if available, or use strerror() otherwise.

Replace all strerror(code) calls with _Py_strerror(code).

• Issue: Calling os.strerror() in parallel is not thread safe on FreeBSD #158893

[vstinner]

On FreeBSD 14, I can reproduce the issue by running test_concurrent_initialization_subinterpreter() of test_datetime in a loop. For example, it crashed at the 4th run:

vstinner@freebsd14$ ./python -m test test_datetime -v -m test_concurrent_initialization_subinterpreter -F
(...)
0:00:05 load avg: 1.85 mem: 37.5 MiB [  4] test_datetime
test_concurrent_initialization_subinterpreter (test.datetimetester.ExtensionModuleTests_Pure.test_concurrent_initialization_subinterpreter) ... skipped 'Not relevant in pure Python'
test_concurrent_initialization_subinterpreter (test.datetimetester.ExtensionModuleTests_Fast.test_concurrent_initialization_subinterpreter) ... FAIL

======================================================================
FAIL: test_concurrent_initialization_subinterpreter (test.datetimetester.ExtensionModuleTests_Fast.test_concurrent_initialization_subinterpreter)
(...)
AssertionError: Process return code is -6 (SIGABRT)
command line: ['/home/vstinner/python/main/python', '-X', 'faulthandler', '-I', '-c', "if True:\n        from concurrent.futures import InterpreterPoolExecutor\n\n        def func():\n            import _datetime\n            print('a', end='')\n\n        with InterpreterPoolExecutor() as executor:\n            for _ in range(8):\n                executor.submit(func)\n        "]

(...)

stderr:
---
Assertion failed: (strlen(arg) == arglen), function _Py_DecodeLocale, file Python/fileutils.c, line 733.
Fatal Python error: Aborted

Current thread 0x000014c00b026010 [InterpreterPoolExec] (most recent call first):
  File "<frozen importlib._bootstrap_external>", line 155 in _path_stat
  File "<frozen importlib._bootstrap_external>", line 161 in _path_is_mode_type
  File "<frozen importlib._bootstrap_external>", line 169 in _path_isfile
  File "<frozen importlib._bootstrap_external>", line 1386 in find_spec
  File "<frozen importlib._bootstrap_external>", line 1251 in _get_spec
  File "<frozen importlib._bootstrap_external>", line 1277 in find_spec
  File "<frozen importlib._bootstrap>", line 1216 in _find_spec
  File "<frozen importlib._bootstrap>", line 1292 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1344 in _find_and_load
  File "/home/vstinner/python/main/Lib/concurrent/futures/_base.py", line 7 in <module>
  (...)

With the fix, the test no longer crash. I ran the test 188 times in 6 minutes.

[vstinner]

Oh, CIFuzz jobs failed with networking issue. Example:

#6 416.3 E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/f/file/libmagic-mgc_5.38-4_amd64.deb Connection failed [IP: 91.189.91.81 80]