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

[Ming-Yi Lai via cfe-commits]

mylai-mtk wrote:

Update:

+ Rebase to latest `main`
+ Remove redundant macro contents
+ Move tests of macros from CodeGen dir to Preprocessor dir
+ Add tests for default branch label scheme
+ Add tests for `-fcf-protection=full`
+ Rewrite PR/commit message

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It looks like some of the new macros are added in gcc already (https://github.com/gcc-mirror/gcc/commit/59a869d7196132ae5257fcb068508561d3526c7d). Is it possible that we restart processing this PR now?

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