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

[Chris Copeland via llvm-commits]

chrisnc wrote:

I've adapted the approach used in the RISC-V backend to this PR and carried over the new test I added before (updated the warning message and changed the expected exit code of the erroneous `llc` invocation to success instead of failure). From local testing, no other tests needed to be changed, but will check CI to confirm.

Would appreciate another review.

I've opted to leave the `clang` warning for this intact, as it deals with more narrow situations and may be more friendly, though there are cases where both will occur.

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