[clang] [Headers][X86] VectorExprEvaluator::VisitCallExpr - allow SSE/AVX2/AVX512 pack intrinsics to be used in constexpr (PR #156003)

[Simon Pilgrim via cfe-commits]

https://github.com/RKSimon requested changes to this pull request.

You need to add handling in InterpBuiltin.cpp as well for the new interpreter - I'd recommend waiting until I've completed #155891 - but I'd also recommend you replace the PackKind enum with a llvm::function_ref callback approach like I've used in #155891 

https://github.com/llvm/llvm-project/pull/156003