[AIX] Check for typedef properly when getting preferred type align

The current check for typedef is naive and doesn't deal with any convoluted cases. This patch makes use of the new 'AlignRequirement' enum field from 'TypeInfo' to determine whether or not this is an 'aligned' attribute on a typedef.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D109387