message: Add dropped ManualDWARFIndex assert()
  D47253 dropped this assertion.
diff: @@ -92,6 +92,9 @@ void ManualDWARFIndex::Index() {
  }
  void ManualDWARFIndex::IndexUnit(DWARFUnit &unit, IndexSet &set) {
  + assert(!unit.GetSymbolFileDWARF()->GetBaseCompileUnit() &&
  + "DWARFUnit associated with .dwo or .dwp should not be indexed directly");
  +
  Log *log = LogChannelDWARF::GetLogIfAll(DWARF_LOG_LOOKUPS);
  if (log) {
  