message: Fix api change in poplar
  Summary: It compiles
  Reviewers: jakeh, davidn
diff: @@ -501,17 +501,17 @@ Status PoplarExecutor::ConfigurePoplarDevice(
  std::to_string(*max_compilation_threads));
  }
  - option_flags_.list([](const std::string& opt, const std::string& val) {
  - VLOG(1) << "Engine option: " << opt << " = " << val;
  - });
  + for (auto opt : option_flags_) {
  + VLOG(1) << "Engine option: " << opt.first << " = " << opt.second;
  + }
  - conv_options_.list([](const std::string& opt, const std::string& val) {
  - VLOG(1) << "Convolution option: " << opt << " = " << val;
  - });
  + for (auto opt : conv_options_) {
  + VLOG(1) << "Convolution option: " << opt.first << " = " << opt.second;
  + }
  - report_options_.list([](const std::string& opt, const std::string& val) {
  - VLOG(1) << "Report option: " << opt << " = " << val;
  - });
  + for (auto opt : report_options_) {
  + VLOG(1) << "Report option: " << opt.first << " = " << opt.second;
  + }
  // Cache Target hash
  std::vector<int64> poplar_target;
  