[llvm] Add diagnostic help for inline asm operand constraint 'H' (PR #86910)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > I think it would be a better API to migrate the print from return bool to Error instead of adding a string out argument
> 
> This is tricky. AsmPrinter::PrintAsmOperand is overridden in each target. 'H' can be slightly different for each target. So when we return to caller of PrintAsmOperand ( generalization) we may need separate special message as per Target. To support it, i added std::string parameter. Is that okay?

Error carries along with it any error string you want 

https://github.com/llvm/llvm-project/pull/86910