gh-98724: Fix type punning issue in Py_SETREF()

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Fix type punning issue in Py_CLEAR(), Py_SETREF() and Py_XSETREF() macros. Don't cast pointers to avoid type punning which cause miscompilation of functions using these macros.

• Issue: Macro Py_CLEAR references argument two times. #98724

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#define _PY_TYPEOF(EXPR) __typeof__(EXPR)

On GCC and clang, typeof() can maybe used. In "GNU mode", typeof is treated as a keyword by the C compiler.

On MSVC, if __typeof__() doesn't work, maybe decltype() can be used instead.

[vstinner]

Ah, building Python with the PR fails on Windows (MSVC) with:

warning C4013: '__typeof__' undefined

[vstinner]

Since MSVC doesn't implement __typeof__(), I don't think that this approach works. I would like the C API to behave the same on all platforms: see #98724 (comment) I close my PR.