This change converts the NVPTX target to use the MC infrastructure
instead of directly emitting MachineInstr instances. This brings
the target more up-to-date with LLVM TOT, and should fix PR15175
and PR15958 (libNVPTXInstPrinter is empty) as a side-effect.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187798 91177308-0d34-0410-b5e6-96231b3b80d8
