Create a new Time structure expressed in UTC from t.

Property definitions

core $ Tm :: gmtime_from_timet
	# Create a new Time structure expressed in UTC from `t`.
	new gmtime_from_timet(t: TimeT) `{
		struct tm *tm;
		tm = gmtime(&t);
		return tm;
	`}
lib/core/time.nit:111,2--116,3