[clang] [PAC] Add support for __ptrauth type qualifier (PR #100830)

[Aaron Ballman via cfe-commits]

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@@ -104,6 +104,7 @@ FEATURE(thread_sanitizer, LangOpts.Sanitize.has(SanitizerKind::Thread))
 FEATURE(dataflow_sanitizer, LangOpts.Sanitize.has(SanitizerKind::DataFlow))
 FEATURE(scudo, LangOpts.Sanitize.hasOneOf(SanitizerKind::Scudo))
 FEATURE(ptrauth_intrinsics, LangOpts.PointerAuthIntrinsics)
+FEATURE(ptrauth_qualifier, LangOpts.PointerAuthIntrinsics)
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AaronBallman wrote:

It does not, see the top of `Features.def`:
```
// FEATURE(...) should be used to advertise support for standard language
// features, whereas EXTENSION(...) should be used for clang extensions. Note
// that many of the identifiers in this file don't follow this rule for backward
// compatibility reasons.
```
Those backwards compatibility reasons are from a time when we only had one way to feature test macros. I think those internal projects should migrate to the correct usage instead of adding this as `FEATURE` for all uses moving forward.

https://github.com/llvm/llvm-project/pull/100830