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

[Ralf Jung via llvm-commits]

RalfJung wrote:

That seems to implement what was sketched above, but I am not familiar with this code so I can't say if there's any possible problems this could cause.

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