[llvm] Add diagnostic help for inline asm operand constraint 'H' (PR #88248)

[via llvm-commits]

mahesh-attarde wrote:

> > Originally https://reviews.llvm.org/D35890
> 
> This is a very different implementation to that

Diagnostic for constraint H was required from this PR. It got pushed out for long, there were code changes which did not merge.
I think this is 3rd attempt 

https://github.com/llvm/llvm-project/pull/88248