[clang] [Clang][TableGen] Add Features to TargetBuiltin (PR #80279)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > The changes seem reasonable to me but I'd feel more comfortable if the functionality was also being used (so that we'd get test coverage verifying its correctness). Do you think it would be reasonable to include the RISCV changes as well?
> 
> Yeah, I separated RISCV changes into another PR(#80280).
> 
> (I used SPR to do the stacked patches, but it seems that it won't refer to its parents or children)

Ah, yeah, I had no idea this was part of a stack of patches. :-( I think this is fine as-is now, thank you!

https://github.com/llvm/llvm-project/pull/80279