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

[Oliver Stannard via llvm-commits]

================
@@ -791,7 +791,9 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
       setAllExpand(MVT::f32);
     if (!Subtarget->hasFP64())
       setAllExpand(MVT::f64);
-  }
+  } else if (TM.Options.FloatABIType == FloatABI::Hard)
----------------
ostannard wrote:

That does look like a better place for this, and already has one check like this, emitted through the `LLVMContext` so that the compiler can exit with a non-zero status code, or report the error through whatever other means it normally used. I think an error is better than a warning for this, because it's not possible to generate the requested code correctly.

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