message: DWARF/DIERef: remove non-const operator<
  It serves no purpose as one can always invoke the const version instead.
diff: @@ -26,8 +26,6 @@ struct DIERef {
  return die_offset < ref.die_offset;
  }
  - bool operator<(const DIERef &ref) { return die_offset < ref.die_offset; }
  -
  explicit operator bool() const {
  return cu_offset != DW_INVALID_OFFSET || die_offset != DW_INVALID_OFFSET;
  }
  