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

[Kito Cheng via cfe-commits]

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@@ -2841,6 +2841,10 @@ def fcf_protection : Flag<["-"], "fcf-protection">, Group<f_Group>,
   Visibility<[ClangOption, CLOption, CC1Option]>,
   Alias<fcf_protection_EQ>, AliasArgs<["full"]>,
   HelpText<"Enable cf-protection in 'full' mode">;
+def fcf_branch_label_scheme_EQ : Joined<["-"], "fcf-branch-label-scheme=">,
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kito-cheng wrote:

```suggestion
def mcf_branch_label_scheme_EQ : Joined<["-"], "mcf-branch-label-scheme=">,
```

Use `m` option rather than `f` option since I assume this should apply to RISC-V only.

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