[clang] [Clang][Sema] Handle invalid variable template specialization whose type depends on itself (PR #134522)

[A. Jiang via cfe-commits]

================
@@ -47,3 +47,21 @@ namespace InvalidInsertPos {
   template<> int v<int, 0>;
   int k = v<int, 500>;
 }
+
+namespace GH51347 {
+  template <typename T>
+  auto p = p<T>; // expected-error {{the type of variable template specialization 'p<int>'}}
----------------
frederick-vs-ja wrote:

It seems that [[temp.res.general]/6](https://eel.is/c++draft/temp.res.general#6) allows us to eagerly diagnose this...

https://github.com/llvm/llvm-project/pull/134522