[clang] [clang] Emit i32 args for __builtin_prefetch (PR #202111)

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mygitljf wrote:

oh, It is closely related, but I don't think it is an exact duplicate. #201623 handles the poison/UB immarg case like `2 >> 32`, while this PR handles valid non-`int` constant expressions like `sizeof`/`ULL` that can still produce non-`i32` LLVM constants. From what I can tell, `EmitScalarOrConstFoldImmArg` still preserves the expression's integer type, so it may not cover the `sizeof`/`ULL` case. 

https://github.com/llvm/llvm-project/pull/202111