[clang] [clang][PAC] ptrauth_qualifier and ptrauth_intrinsic should only be available on Darwin (PR #153912)

[Oliver Hunt via cfe-commits]

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@@ -1089,6 +1089,7 @@ static void ComputeDATE_TIME(SourceLocation &DATELoc, SourceLocation &TIMELoc,
 /// specified by the identifier as a standard language feature.
 static bool HasFeature(const Preprocessor &PP, StringRef Feature) {
   const LangOptions &LangOpts = PP.getLangOpts();
+  const TargetInfo &Target = PP.getTargetInfo();
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ojhunt wrote:

It's used in the FEATURE() macro below for the darwin restriction on the feature checks

https://github.com/llvm/llvm-project/pull/153912