This support is _very_ rudimentary, just enough to get some basic data
into the CodeView debug section.
Left to do is:
- Use the combined opcodes to save space.
- Do something about code offsets.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259230 91177308-0d34-0410-b5e6-96231b3b80d8