[3.14] gh-158893: Make os.strerror() thread-safe (#159120)

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• The Python C API should only define macros with a name starting wit Py #157695: Parse also _Py_HAVE_xxx variables in sysconfig (gh-157695: Parse also _Py_HAVE_xxx variables in sysconfig #158926)

Add parse_config_h() tests to test_sysconfig.

(cherry picked from commit 978a8be)

• Calling os.strerror() in parallel is not thread safe on FreeBSD #158893: Make os.strerror() thread-safe (gh-158893: Make os.strerror() thread-safe #158927)

Make os.strerror() thread-safe: use the reentrant strerror_r() function if available.

• The configure script now checks if strerror_r() is supported.

• Add a stress test to test_free_threading.test_os (new module).

• Add a comment on decode_current_locale() assertion which fails if the input string is mutated.

• Add an assertion to _Py_DecodeLocale() to detect if the input string was mutated during the function call.

• Calling os.strerror() in parallel is not thread safe on FreeBSD #158893: Add internal _Py_strerror() function (gh-158893: Add internal _Py_strerror() function #158982)

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).

(cherry picked from commit 15dd735) (cherry picked from commit c774d15)

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Note: the sysconfig backport doesn't strip quotes from variables (no behavior change), it's different from 3.15 and main branches.