[clang] [Clang] Add __builtin_selectvector and use it for AVX512 intrinsics (PR #91306)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> clang already supports `?:` with a vector condition; does this add anything new on top of that?

This works with bool vectors. I didn't realize you could use the ternary operator, since I only tested with them. I guess we could extend the ternary operator to accept bool vectors as well. Any thoughts?

https://github.com/llvm/llvm-project/pull/91306