SLPVectorizer: start constructing chains at stores that are not power of two.
The type <3 x i8> is a common in graphics and we want to be able to vectorize it.

This changes accelerates bullet by 12% and 471_omnetpp by 5%.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184317 91177308-0d34-0410-b5e6-96231b3b80d8