[clang] [llvm] [RISCV] Make zvknha a subset of zvknhb (PR #178680)

[Sam Elliott via cfe-commits]

lenary wrote:

> > I'm not sure the unified db is verifying our extension implication information. I think it just does encoding information.
> 
> Ok. Is it something that might be checked in the future? Maybe I should learn more about unified-db?

I think unified db does have enough information to verify this in the future. I just don't think it's implemented yet.

https://github.com/llvm/llvm-project/pull/178680