[X86][SSE] Improve PACKSS shuffle tests to better match codegen from D61129
[X86][SSE] Improve PACKSS shuffle tests to better match codegen from D61129

D61129 creates 'concat + trunc' style patterns (at the 128-bit subvector level)

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@369209 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm