Add DwarfRegNum

[reitowo]

// General-purpose registers
foreach I = 0-31 in {
  def R#I : GRi<I, "r"#I>, DwarfRegNum<[I]>;
}

Otherwise, ./llc sum.ll -filetype=obj -march=m88k will fail.

[redstar]

What error message to you get?
Adding the register number to DWARF code has no influence when no debug code is emitted. The sum.ll does not contain debug code at all (assuming you are using the file from chapter 9).