[llvm] [ARM] Emit a warning when the hard-float ABI is enabled but can't be used. (PR #111334)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

Personally I don't have any fundamental objections to a diagnostic given that the existing clang diagnostic has been kept in place. As maintainers I think the final say needs to be with @ostannard and @davemgreen . 

I'm wondering if there's any surrounding context that can used to make the warning more useful. Right now it seems to be appearing once per Subtarget. I've left a more specific comment where more context is available.

https://github.com/llvm/llvm-project/pull/111334