- We now always output dwarf3 so we can use DW_OP_call_frame_cfa and avoid
  construction location lists, but just reuse the callframe info lists.
- Backends have to emit debug info as callframe calculation changes:
  The ia32 backend has a preliminary implementation which assumes esp
  offset of frame_type_size at the beginning of a block (currently
  always true), the no-omit-fp mode assumes ebp relative addressing
  (which is correct except for the prolog/epilogue insns)