ObjFW  Check-in [f5c8495a33]

#ifdef STRUCT_TM_HAS_TM_GMTOFF
		if (tm.tm_gmtoff != 0)
			@throw [OFInvalidFormatException
			    exceptionWithClass: isa];
#endif

		/* Years */
		seconds = (tm.tm_year - 70) * 31536000;
		seconds = (time_t)(tm.tm_year - 70) * 31536000;
		/* Leap years */
		seconds += ((tm.tm_year / 4) - 17) * 86400;
		seconds += (((tm.tm_year + 1900) / 4) - 492) * 86400;
		seconds -= (((tm.tm_year + 1900) / 100) - 19) * 86400;
		seconds += (((tm.tm_year + 1900) / 400) - 4) * 86400;
		/* Months */
		if (tm.tm_mon < 0 || tm.tm_mon > 12)
			@throw [OFInvalidFormatException
			    exceptionWithClass: isa];
		seconds += month_to_day_of_year[tm.tm_mon - 1] * 86400;
		/* Days */
		seconds += (tm.tm_mday - 1) * 86400;