[clang] Add support for anyAppleOS availability (PR #181953)

[Akira Hatanaka via cfe-commits]

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@@ -2697,6 +2698,70 @@ static void handleAvailabilityAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     }
   }
 
+  // Handle anyAppleOS specially: create implicit platform-specific attributes
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ahatanak wrote:

OK, let's discuss this after merging this PR.

https://github.com/llvm/llvm-project/pull/181953