[issue40302] Add _Py_bswap32() function to pyport.h

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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pull_requests: +18913
pull_request: https://github.com/python/cpython/pull/19573

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40302>
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