[clang] [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:

@statham-arm I tried the example of the weird diagnostic. If you pass `-g`, the call site is shown in the output as expected. This is because without `-g` there are no `!dbg` attachments on the IR at the call site to use in the diagnostic, only the function itself. I agree the message is confusing in the case where this is not present though.

```bash
$ build/bin/clang --target=armv8a-none-eabi -mfloat-abi=hard -c zz.c -g
zz.c:3:12: error: call to 'g' expects a hard-float calling convention, but floating-point
      registers are unavailable
    3 |     return g() + 1;
      |            ^
1 error generated.
```

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