[clang] [Clang][RISCV] Add preprocessor macros for Zicfilp CFI scheme (PR #109600)

[Kito Cheng via cfe-commits]

kito-cheng wrote:

> @kito-cheng I need your input on this, since this would require a few updates on various PRs to the RISC-V specs.

Yeah, I just chat with Craig, I think that right way to go, and actually the PR in riscv-toolchain-conventions I has implicitly allow that, I mean I only write `-fcf-protection=return` require `zimop`, and didn't say `-fcf-protection=branch` require `zicfilp`, so yeah, go ahead to drop the requirement of `zicfilp`, Craig and me will fix that on the back-end side :P


[1] https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/54  

https://github.com/llvm/llvm-project/pull/109600