[clang] [clang] Allow class with anonymous union member to be const-default-constructible even if a union member has a default member initializer (#95854) (PR #96301)

[Shafik Yaghmour via cfe-commits]

================
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+
+struct A {
----------------
shafik wrote:

We should also test this case: 

```cpp
struct A {
  union {
    int n;
    int m=0;
  };
};
const A a;
```

https://github.com/llvm/llvm-project/pull/96301