[clang] [clang][ExtractAPI] Compute inherited availability information (PR #103040)

[Cyndy Ishida via cfe-commits]

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@@ -16,33 +16,101 @@
 #include "clang/AST/Decl.h"
 #include "clang/Basic/TargetInfo.h"
 
-namespace clang {
+namespace {
+
+struct AvailabilitySet {
+  llvm::SmallVector<clang::AvailabilityInfo> Availabilities;
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cyndyishida wrote:

Can you mark this private, its not clear otherwise that one should be going through `insert`

https://github.com/llvm/llvm-project/pull/103040