[clang] [Clang] Emit a diagnostic note at the class declaration when the method definition does not match any declaration. (PR #110638)

[Vlad Serebrennikov via cfe-commits]

================
@@ -597,9 +597,10 @@ namespace cwg336 { // cwg336: yes
         void mf2();
       };
     };
-    template<> template<class X> class A<int>::B {};
+    template<> template<class X> class A<int>::B {}; // #defined-here-cwg336
----------------
Endilll wrote:

```suggestion
    template<> template<class X> class A<int>::B {}; // #cwg336-B
```

https://github.com/llvm/llvm-project/pull/110638