Wrong macro is used for free-threaded GC prefetch check for 32-bit MSVC

[lpyu001]

Bug report

Bug description

In Python/gc_free_threading.c, the MSVC architecture check contains a typo:

cpython/Python/gc_free_threading.c

Line 551 in 6b97452

#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_I86)) && !defined(_M_ARM64EC)

_M_I86 should be _M_IX86, which is the macro defined by 32-bit MSVC. Because of this typo, 32-bit free-threaded builds select the no-op prefetch fallback.

This only affects performance; GC correctness is unchanged.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-157906: fix an incorrect architecture macro check in free-threaded GC  #157907