Add handling for these additional `MCValue`s:
* `.immediate` - lower to `DW.OP.consts` or `DW.OP.constu` depending
  on signedness followed by popping off the DWARF stack with
  `DW.OP.stack_value`
* `.undef` - lower to `DW.OP.implicit_value`
* `.none` - lower to `DW.OP.lit0` followed by popping off the DWARF
  stack with `DW.OP.stack_value`

For any remaining unhandled case, we generate `DW.OP.nop` in order
not to mess up remaining DWARF info.