[clang] Fix __builtin_object_size calculation for references of unknown origin in C++23 (PR #157778)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Try the following with -std=c++23 -Winvalid-constexpr:

```
constexpr int f(int &a) {
  return 1 / (__builtin_object_size(&a, 0) - 4);
}
int a[2];
static_assert(f(a[0]) == 0);
```

https://github.com/llvm/llvm-project/pull/157778