[clang] [Clang] prevent errors for deduction guides using deduced type aliases (PR #117450)

[Younan Zhang via cfe-commits]

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@@ -33,7 +33,7 @@ template<template<typename> typename TT> struct E { // expected-note 2{{template
 };
 
 A(int) -> int; // expected-error {{deduced type 'int' of deduction guide is not a specialization of template 'A'}}
-template <typename T> A(T)->B<T>;         // expected-error {{deduced type 'B<T>' (aka 'A<T>') of deduction guide is not written as a specialization of template 'A'}}
+template <typename T> A(T)->B<T>;
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zyn0217 wrote:

I think this is probably sufficient to prove GH54909 has been fixed?

https://github.com/llvm/llvm-project/pull/117450