[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

[via cfe-commits]

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@@ -5538,7 +5539,8 @@ class Sema final : public SemaBase {
   /// parameters present at all, require proper matching, i.e.
   ///   template <> template \<class T> friend class A<int>::B;
   Decl *ActOnFriendTypeDecl(Scope *S, const DeclSpec &DS,
-                            MultiTemplateParamsArg TemplateParams);
+                            MultiTemplateParamsArg TemplateParams,
+                            SourceLocation FriendEllipsisLoc);
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cor3ntin wrote:

```suggestion
                            SourceLocation EllipsisLoc);
```

https://github.com/llvm/llvm-project/pull/101448