[clang] [clang][bytecode] Implement ia32_select* builtins (PR #154758)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

There are a decent number of x86 intrinsics I'm hoping to support in constexpr - we'll have to see if we step over any kind of tolerance limit :/ 

https://github.com/llvm/llvm-project/pull/154758