[clang] [Clang] Handle structs with inner structs and no fields (PR #89126)

[Eli Friedman via cfe-commits]

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

We should probably apply the same fix to CountCountedByAttrs.

Along those lines, we should be able to handle:

```
struct bar {
  int count;
  int array[] __attribute__((counted_by(count)));
};
struct foo { struct bar x; };
void init(void * __attribute__((pass_dynamic_object_size(0))));
void test1(struct foo *p) {
  init(p);
}
```

https://github.com/llvm/llvm-project/pull/89126