[clang] [clang-tools-extra] [lldb] [clang] implement CWG1558 and CWG2064: instantiation-dependency improvements (PR #190495)

[Vlad Serebrennikov via cfe-commits]

================
@@ -64,6 +64,19 @@ namespace cwg2061 { // cwg2061: 2.7
 #endif // C++11
 } // namespace cwg2061
 
+namespace cwg2064 { // cwg2064: 23
+#if __cplusplus >= 201103L
+  template<typename T> struct X {
+    template<typename U> struct Y {};
+  };
+  template<typename T> void g() {
+    X<decltype(sizeof(T))>::Y<int> y; // ok
----------------
Endilll wrote:

```suggestion
    typename X<decltype(sizeof(T))>::template Y<int> y; // ok
```
Or could it be that your PR somehow makes those keywords optional here?

https://github.com/llvm/llvm-project/pull/190495