GeezerVison

Fixes #157649.

Use the existing memcpy() implementations of Py_CLEAR, Py_SETREF and Py_XSETREF for C++, as suggested in the issue discussion. decltype() can bind their temporary to an array element or reference, so overwriting the destination decrements the wrong pointer. The C paths are unchanged.

The C++ regression exercises all three macros with array elements, references, NULL destinations, single evaluation and concrete object pointers. Py_CLEAR() also runs in the limited-API build. Thanks to Lucas Colley for the report/bisection and Victor Stinner for the fallback approach.

Validation

Original before/after run, Ubuntu x86-64, GCC/g++ 13.3, debug CPython 3.16 built from 8542958:

• Test-only C++11 regression fails on unchanged headers with the old-object refcount assertion after Py_SETREF.
• Fixed test_cppext and test_cext: 14 passed, 1 Windows-only C++14 skip. Covers C++03/C++11, limited API, C99/C11 and strict compiler flags.
• git diff --check passes.

That fork run covered only the extension suites. Subsequently, upstream Tests run 35367131812 completed successfully on head a66a922; lint and label checks also pass. The follow-up commit changes only the requested source comment. No NumPy rebuild is claimed.

AI assistance: ChatGPT assisted with implementation and validation.

• Issue: Py_CLEAR/Py_SETREF() regression on the main branch with C++: SEGV with simple numpy program #157649