message: Abbreviation declarations are required to have non-null tags.
  Treat a null tag as an error.
diff: @@ -34,11 +34,9 @@ DWARFAbbreviationDeclaration::extract(const DWARFDataExtractor &data,
  m_attributes.clear();
  m_tag = data.GetULEB128(offset_ptr);
  - if (m_tag == DW_TAG_null) {
  - // FIXME: According to the DWARF spec this may actually be malformed.
  - // Should this return an error instead?
  - return DWARFEnumState::Complete;
  - }
  + if (m_tag == DW_TAG_null)
  + return llvm::make_error<llvm::object::GenericBinaryError>(
  + "abbrev decl requires non-null tag.");
  m_has_children = data.GetU8(offset_ptr);
  