[clang] [AArch64][FMV] Enable PAuth and BTI hardening of resolver functions (PR #141573)

[Anatoly Trosinenko via cfe-commits]

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@@ -4652,6 +4659,7 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
                                   "", Resolver, &getModule());
     GIF->setName(ResolverName);
     SetCommonAttributes(FD, GIF);
+    SetResolverAttrs(cast<llvm::Function>(*Resolver));
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atrosinenko wrote:

Reused `setTargetAttributes`, thank you! If I understand it correctly, it should be safer not to pass any `Decl` to `setTargetAttributes`, as otherwise the implementation might inspect target-specific function attributes and use them for the resolver (which can correspond to one or multiple declarations), and we want to only set the bare minimum attributes instead.

https://github.com/llvm/llvm-project/pull/141573