SLPVectorizer: Fix a bug in the code that generates extracts for values with multiple users.
The external user does not have to be in lane #0. We have to save the lane for each scalar so that we know which vector lane to extract.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181674 91177308-0d34-0410-b5e6-96231b3b80d8