[clang] [clang] Restrict use of scalar types in vector builtins (PR #119423)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

> Would be good to also update the documentation for the builtins the clarify the behavior.

I've added some words to that effect. Is that what you had in mind?

https://github.com/llvm/llvm-project/pull/119423