[clang] [CIR] Upstream vec shuffle builtins in CIR codegen (PR #169178)

[Thibault Monnier via cfe-commits]

Thibault-Monnier wrote:

Thank you for the reviews!

In fact, there _were_ tests for the `pshufd` / `vpermilp` in the incubator, so I upstreamed them.

I'll keep this PR for the `shuf` builtins, and move the others to a different branch.

https://github.com/llvm/llvm-project/pull/169178