Use fmt::localtime instead of thread-unsafe std::localtime

fmt::localtime is also less awkward to use compared to std::localtime.

Source/Core/Common/SettingsHandler.cpp

@@ -140,6 +140,6 @@ std::string SettingsHandler::GenerateSerialNumber()
   // Must be 9 characters at most; otherwise the serial number will be rejected by SDK libraries,
   // as there is a check to ensure the string length is strictly lower than 10.
   // 3 for %j, 2 for %H, 2 for %M, 2 for %S.
-  return fmt::format("{:%j%H%M%S}", *std::localtime(&t));
+  return fmt::format("{:%j%H%M%S}", fmt::localtime(t));
 }
 }  // namespace Common