Simplify the code a bit.

The compact unwind registers were defined in two different
places. It's better just to place them in the function that uses them
and specify that this is a 64-bit or 32-bit machine.

No functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181529 91177308-0d34-0410-b5e6-96231b3b80d8