[X86][SSE2] Fix zero/any extension shuffles that don't start from the first element

Fix for D12561 - we weren't correctly ensuring that the base element for extension was moved to start on a boundary suitable for UNPCKL/H

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248536 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed