[clang] [clang][CodeGen] Fix MSVC ABI for classes with non static data members of reference type (PR #90547)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

Maybe we should just be testing if the copy-assignment operator is deleted?  For reference, MSVC also returns the following indirectly:

```
struct Test
{
    int x;
    Test& operator=(const Test&) = delete;
};
Test foo();
Test test(Test x)
{
  return x;
}
```

https://github.com/llvm/llvm-project/pull/90547