When diagnosing taking address of packed members skip __unaligned-qualified expressions

Given that we have already explicitly stated in the qualifier that the
expression is __unaligned, it makes little sense to diagnose that the address
of the packed member may not be aligned.

Differential Revision: https://reviews.llvm.org/D30884



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@297620 91177308-0d34-0410-b5e6-96231b3b80d8