- Added support to turn "vector clear elements", e.g. pand V, <-1, -1, 0, -1>

- Added support to turn "vector clear elements", e.g. pand V, <-1, -1, 0, -1>
to a vector shuffle.
- VECTOR_SHUFFLE lowering change in preparation for more efficient codegen
of vector shuffle with zero (or any splat) vector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27875 91177308-0d34-0410-b5e6-96231b3b80d8