[X86] Add tests for ATOMIC_LOAD_OP EFLAGS reuse. NFC.
[X86] Add tests for ATOMIC_LOAD_OP EFLAGS reuse. NFC.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@265448 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit a4e82226ecff4f98e4f78cdbafd2702011a7ec12)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm