message: Fix ambiguous conversion
  Summary: Mollify some versions of GCC, hopefully.
diff: @@ -1199,8 +1199,9 @@ int main(int argc, char* argv[]) {
  // now that all the timers are done running, we can collect the data
  stats["output_stats"]["time_stats"] = get_times();
  auto vm_stats = get_mem_stats();
  - stats["output_stats"]["mem_stats"]["vm_peak"] = vm_stats.vm_peak;
  - stats["output_stats"]["mem_stats"]["vm_hwm"] = vm_stats.vm_hwm;
  + stats["output_stats"]["mem_stats"]["vm_peak"] =
  + (Json::UInt64)vm_stats.vm_peak;
  + stats["output_stats"]["mem_stats"]["vm_hwm"] = (Json::UInt64)vm_stats.vm_peak;
  {
  std::ofstream out(stats_output_path);
  out << stats;
  