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

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

I've found one edge case that I would expect to work, but triggers the error message.

I don't think it will be common, the only reason I can think of to use it is some code that is doing run-time selection.

It is more common to have a single implementation that uses floating point registers internally, but has a hard-float and soft-float (softfp) wrappers. 

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