[DAGCombine] Add test cases to show that DAG combining an OR of two shuffles with zero vectors doesn't work if the zero vector is the first operand of the shuffle. Fix coming in a follow up patch.
[DAGCombine] Add test cases to show that DAG combining an OR of two shuffles with zero vectors doesn't work if the zero vector is the first operand of the shuffle. Fix coming in a follow up patch.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@274096 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm