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

[Wang Pengcheng via cfe-commits]

wangpc-pp 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(https://github.com/llvm/llvm-project/pull/80280).

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