[clang] [Clang] VectorExprEvaluator::VisitCallExpr / InterpretBuiltin - Allow shufps/pd shuffles intrinsics to be used in constexpr (PR #164078)

[Simon Pilgrim via cfe-commits]

https://github.com/RKSimon commented:

We seem to be creating a lot of shuffle decoding helper functions - it'd be great if some of them could share more of the code, or maybe even convert some to a callback system? The callback returns the shuffle source index given the immediate mask and the element index.

https://github.com/llvm/llvm-project/pull/164078