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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

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?

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