[clang] [clang][AST] fix dereference on class/struct layouts check. (PR #83686)

[Jack Ren via cfe-commits]

bjrjk wrote:

Hello, this is a mininal reproducer execute with `clang++ -Xclang -fdump-record-layouts-complete test.cpp`:
```cpp
template <class _Tp, _Tp __v>
struct integral_constant {
  static constexpr const _Tp value = __v;
  typedef integral_constant type;
};

template <bool _Val>
using _BoolConstant = integral_constant<bool, _Val>;

template <class _Tp, class _Up>
struct is_same : _BoolConstant<__is_same(_Tp, _Up)> {};
```

https://github.com/llvm/llvm-project/pull/83686