[AIX] Use less than or equal to for some alignment tests on AIX

On AIX the alignment implementation has the storage aligned to the
preferred alignment instead of the alignment of a type. Macro guard
these tests for AIX and have them pass when the "reference alignment" is
less than or equal to the alignment observed. In other words, the
alignment applied is at least as strict as the required alignment.

Reviewed By: hubert.reinterpretcast

Differential Revision: https://reviews.llvm.org/D104786