[llvm] [NFC] Add useFPRegsForHalfType(). (PR #74147)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

Kind of. I'm only trying to use `f32` to maintain compatibility with current LLVM, which uses it implicitly for function arguments and return values because that's what it's promoted to. Any place that doesn't affect compatibility, it doesn't matter whether it's promoted to `i16` or to `f32` so long as the promotion is done correctly, and reversed correctly. I'll have a look at implementing it in the way that you suggest.

https://github.com/llvm/llvm-project/pull/74147