[clang] [Clang] Fix crash in alignment builtins with null pointers (PR #224549)

[Timm Baeder via cfe-commits]

tbaederr wrote:

So,
```c++
   _Static_assert(__builtin_is_aligned((void *)33, 32), "");
```
this is supposed to....? Work? Not work?

```c++
   _Static_assert(__builtin_is_aligned((void *)32, 32), "");
```
this works, but isn't the alignment of both of those pointers the same? Are we really supposed to treat an integer casted to a pointer just like an integer?

https://github.com/llvm/llvm-project/pull/224549