X86 Tests: Unsigned saturation subtraction tests. NFC.
X86 Tests: Unsigned saturation subtraction tests. NFC.

Summary:
Adding tests for D37534.

Commit on behalf of julia.koval@intel.com

Reviewers: n.bozhenov, zvi, spatel, DavidKreitzer

Reviewed By: zvi

Differential Revision: https://reviews.llvm.org/D37510

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@314305 91177308-0d34-0410-b5e6-96231b3b80d8

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