GlobalISel: tidy up def/use test. NFC.
GlobalISel: tidy up def/use test. NFC.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@293545 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 38336fee7d917776e6d32e14d07542fab57fbeeb)

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