gh-157906: fix an incorrect architecture macro check in free-threaded GC (gh-157907)

Fix typo in free-threaded GC prefetch check for 32-bit x86 MSVC.

Author: lpyu001

Misc/NEWS.d/next/Windows/2026-09-21-20-54-37.gh-issue-157906.RlyLkY.rst

@@ -0,0 +1,2 @@
+Fix an incorrect architecture macro check that prevented CPU prefetching in
+the free-threaded garbage collector on 32-bit Windows builds.

Python/gc_free_threading.c

@@ -548,7 +548,7 @@ static_assert(BUFFER_HI < BUFFER_SIZE &&
     #define PREFETCH_T1(ptr)  __builtin_prefetch(ptr, 0, 2)
     #define PREFETCH_T2(ptr)  __builtin_prefetch(ptr, 0, 1)
     #define PREFETCH_NTA(ptr)  __builtin_prefetch(ptr, 0, 0)
-#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_I86)) && !defined(_M_ARM64EC)
+#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86)) && !defined(_M_ARM64EC)
     #include <mmintrin.h>
     #define PREFETCH_T0(ptr)  _mm_prefetch((const char*)(ptr), _MM_HINT_T0)
     #define PREFETCH_T1(ptr)  _mm_prefetch((const char*)(ptr), _MM_HINT_T1)