[X86] Add v8i64->v8i8 ssat/usat/packus truncate tests to min-legal-vector-width.ll
[X86] Add v8i64->v8i8 ssat/usat/packus truncate tests to min-legal-vector-width.ll

I wonder if we should split the v8i8 stores in order to form
two v4i8 saturating truncating stores. This would remove the
unpckl needed to concatenated the v4i8 results to make a
single store.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@374519 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm