[clang] [llvm] [X86] Extend kCFI with a 3-bit arity indicator (PR #121070)

[Miguel Ojeda via llvm-commits]

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@@ -254,6 +254,7 @@ FEATURE(is_trivially_constructible, LangOpts.CPlusPlus)
 FEATURE(is_trivially_copyable, LangOpts.CPlusPlus)
 FEATURE(is_union, LangOpts.CPlusPlus)
 FEATURE(kcfi, LangOpts.Sanitize.has(SanitizerKind::KCFI))
+FEATURE(kcfi_x86_arity, LangOpts.Sanitize.has(SanitizerKind::KCFI))
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ojeda wrote:

For Kconfig, most features are discovered via testing a flag (e.g. `-fsanitize=kcfi`), but if the kernel needs `__has_feature()` anyway here, then that can also be used, yeah. For `rustc`, we can do similar tests too (and since we only support one kind of Rust compiler so far, versions checks can be a fallback option too).

https://github.com/llvm/llvm-project/pull/121070