[Sema] Reject array element types whose sizes aren't a multiple of their

alignments

In the following code, the first element is aligned on a 16-byte
boundary, but the remaining elements aren't:

```
typedef char int8_a16 __attribute__((aligned(16)));
int8_a16 array[4];
```

Currently clang doesn't reject the code, but it should since it can
cause crashes at runtime. This patch also fixes assertion failures in
CodeGen caused by the changes in https://reviews.llvm.org/D123649.

Differential Revision: https://reviews.llvm.org/D133711