[clang] [Clang] Added explanation why a is constructible evaluated to false. (PR #143309)

[Vlad Serebrennikov via cfe-commits]

================
@@ -564,11 +564,12 @@ struct A {
 namespace ex2 {
 #if __cplusplus >= 201103L
 struct Bar {
-  struct Baz {
+  struct Baz { // #Baz
----------------
Endilll wrote:

```suggestion
  struct Baz { // #cwg1890-Baz
```

https://github.com/llvm/llvm-project/pull/143309