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

[Chris Copeland via cfe-commits]

chrisnc wrote:

> It looks like there is already a warning for this in clang, it only triggers from -mfloat-abi=hard though: https://godbolt.org/z/dcaz8had4. Could it be made to work with any hard-float env? And maybe be made an error down-gradable to a warning?
> 
> Generally clang-level warnings/errors are more user friendly then the llvm-level errors (but both may be useful for other frontends).

That seems like a decent improvement to the clang warning, but the backend behavior of still emitting the VFP ABI tag in this case seems like a bug, regardless of the frontend, so IMO codegen should be aborted in this situation.

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