MachineVerifier: Improve register operand checks
MachineVerifier: Improve register operand checks

This fixes cases where we wouldn't perform various register operand
checks just because we didn't happen to have a definition in the
MCInstrDesc. This changes the code to only skip the tests that actually
depend on the MCInstrDesc definition.

This makes the machine verifier spot the problem from
https://llvm.org/PR33071 after the pass that actually caused it.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@319141 91177308-0d34-0410-b5e6-96231b3b80d8

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