[clang] [Win/X86] Make _m_prefetch[w] builtins to avoid winnt.h conflicts (PR #115099)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

Maybe a stupid question, but couldn't we make the function simply `__attribute__((overloadable, enable_if(true, ""))) `?

https://github.com/llvm/llvm-project/pull/115099