mktime method
Converts a local Tm structure to a Unix timestamp (time_t).
This also normalizes the values in timeptr.
Implementation
int mktime(Tm timeptr) {
final dt = timeptr.toDateTime(isUtc: false);
final normalized = Tm.fromDateTime(dt);
timeptr.tm_sec = normalized.tm_sec;
timeptr.tm_min = normalized.tm_min;
timeptr.tm_hour = normalized.tm_hour;
timeptr.tm_mday = normalized.tm_mday;
timeptr.tm_mon = normalized.tm_mon;
timeptr.tm_year = normalized.tm_year;
timeptr.tm_wday = normalized.tm_wday;
timeptr.tm_yday = normalized.tm_yday;
timeptr.tm_isdst = normalized.tm_isdst;
return dt.millisecondsSinceEpoch ~/ 1000;
}