[DAGCombiner] Don't accept -1 sdiv divisors in sdiv-by-pow2 vector expansion (PR37119)

Temporary fix until I've managed to get D45806 updated - both +1 and -1 special cases need to be properly supported.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335637 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed