Mark vector loops as already vectorized

Make sure we mark all loops (scalar and vector) when vectorizing,
so that we don't try to vectorize them anymore. Also, set unroll
to 1, since this is what we check for on early exit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193349 91177308-0d34-0410-b5e6-96231b3b80d8
Reverting my r193344 checkin due to build breakage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193350 91177308-0d34-0410-b5e6-96231b3b80d8