Extend bounds inference to handle relative alignment.

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#328

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We need to make sure that bounds inference properly handles bounds with relative alignment. In addition, we need to introduce relative alignment requirements at casts of array_ptrs.

Normally we can omit relative alignment in a bounds declaration for some array_ptr. It is assumed to be T. So first we face the question of whether to always make relative alignment explicit during bounds inference.

Second, when a pointer p with some type array_ptr is cast to have type array_ptr, p retains its original relative alignment. If no relative alignment has been specified for p, than its relative alignment is sizeof(T).