Make the alignedload and alignedstore patterns always require 16-byte
alignment. This way when they are used in the "Fs" instructions, in which
a vector instruction is used for a scalar purpose, they can still require
the full vector alignment. And add a regression test for this.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40555 91177308-0d34-0410-b5e6-96231b3b80d8
