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: https://llvm.org/svn/llvm-project/llvm/trunk@314305 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed