[clang] [clang] Improve diagnostics for vector builtins (PR #125673)

[Farzon Lotfi via cfe-commits]

https://github.com/farzonl approved this pull request.

As far as the HLSL changes go. This looks fine to me. Approved! Please wait for other stakholders before merging.

https://github.com/llvm/llvm-project/pull/125673