By default LLVM thinks very large vectors get aligned to their size when
passed across functions. Unfortunately no-one told the ARM backend so it
doesn't trigger stack realignment and so accesses can cause the usual
misalignment issues (e.g. a data abort).
This changes the ABI alignment to the stack alignment, which in practice
(and as a bonus) also coincides with the alignment "natural" vectors get.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331451 91177308-0d34-0410-b5e6-96231b3b80d8
