[MSVC, ARM64] Fix signature for __prefetch (#93235)

#67174 added the `__prefetch` intrinsic, however it used the wrong
signature: the argument should be `const void*`, not `void*`.

Docs:
https://learn.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics?view=msvc-170#:~:text=__prefetch

Unfortunately, this can't be backported (there are no more 18.x
releases, and this change is a breaking change), so I'll see if I can
get a workaround added on MSVC's side for Clang 18.

Author: dpaoliello

clang/include/clang/Basic/BuiltinsAArch64.def

@@ -290,7 +290,7 @@ TARGET_HEADER_BUILTIN(_CountLeadingZeros64, "UiULLi", "nh", INTRIN_H, ALL_MS_LAN
 TARGET_HEADER_BUILTIN(_CountOneBits, "UiUNi", "nh", INTRIN_H, ALL_MS_LANGUAGES, "")
 TARGET_HEADER_BUILTIN(_CountOneBits64, "UiULLi", "nh", INTRIN_H, ALL_MS_LANGUAGES, "")
 
-TARGET_HEADER_BUILTIN(__prefetch, "vv*", "nh", INTRIN_H, ALL_MS_LANGUAGES, "")
+TARGET_HEADER_BUILTIN(__prefetch, "vvC*", "nh", INTRIN_H, ALL_MS_LANGUAGES, "")
 
 #undef BUILTIN
 #undef LANGBUILTIN

clang/lib/Headers/intrin.h

@@ -378,7 +378,7 @@ unsigned int _CountLeadingSigns64(__int64);
 unsigned int _CountOneBits(unsigned long);
 unsigned int _CountOneBits64(unsigned __int64);
 
-void __cdecl __prefetch(void *);
+void __cdecl __prefetch(const void *);
 #endif
 
 /*----------------------------------------------------------------------------*\