message: Add time cast to SymbolFileDWARFDebugMap
  After TimePoint's precision was increased in LLVM we started seeing
  failures because the modification times didn't match. This adds a time
  cast to ensure that we're comparing TimePoints with the same level of
  precision.
  Based on r347660 on llvm.org
diff: @@ -425,7 +425,10 @@ Module *SymbolFileDWARFDebugMap::GetModuleByCompUnitInfo(
  FileSpec oso_file(oso_path, false);
  ConstString oso_object;
  if (oso_file.Exists()) {
  - auto oso_mod_time = FileSystem::GetModificationTime(oso_file);
  + // The modification time returned by the FS can have a higher precision
  + // than the one from the CU.
  + auto oso_mod_time = std::chrono::time_point_cast<std::chrono::seconds>(
  + FileSystem::GetModificationTime(oso_file));
  if (oso_mod_time != comp_unit_info->oso_mod_time) {
  obj_file->GetModule()->ReportError(
  "debug map object file '%s' has changed (actual time is "
  