[AArch64] Add more tests for 64-bit immediate lowering.
[AArch64] Add more tests for 64-bit immediate lowering.

This adds a some more tests, and adds some notes to tests which are using
a suboptimal lowering.

The constants with suboptimal lowerings seem to be relatively rare in
practice, but it might be a fun project to work on improvements.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@331304 91177308-0d34-0410-b5e6-96231b3b80d8

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