LoopVectorizer: Fix 15830. When scalarizing and unrolling stores make sure that the order in which the elements are scalarized is the same as the original order.
This fixes a miscompilation in FreeBSD's regex library.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180121 91177308-0d34-0410-b5e6-96231b3b80d8