[ARM] Set AddPristinesAndCSRs to expandCMP_SWAP LivePhysRegs.
[ARM] Set AddPristinesAndCSRs to expandCMP_SWAP LivePhysRegs.

We run after PEI.
Found via inspection; no obvious testcase.

Follow-up to r266679.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@267781 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 5678798442afca31695f108912278bb4af28296d)

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