linux: free datetime interface from tzset

New OSX Date interface had dropped old Windows specific date tests. Do the same for Linux

Author: obastemur

lib/Runtime/PlatformAgnostic/Platform/Linux/DateTime.cpp

@@ -139,7 +139,7 @@ namespace DateTime
  struct tm time_tm = {0};
  bool leap_added;
  YMD_TO_TM(ymd, &time_tm, &leap_added);
- timelocal(&time_tm); // get zone name for the given date
+ mktime(&time_tm); // get zone name for the given date
  CopyTimeZoneName(data.standardName, &data.standardNameLength, time_tm.tm_zone);
  *nameLength = data.standardNameLength;
  return data.standardName;
@@ -160,8 +160,7 @@ namespace DateTime
  // tm doesn't have milliseconds
  int milliseconds = local->time % 1000;
 
- tzset();
- time_t utime = timelocal(&local_tm);
+ time_t utime = mktime(&local_tm);
  if (local_tm.tm_isdst)
  {
  utime -= 3600;
@@ -188,8 +187,8 @@ namespace DateTime
  // tm doesn't have milliseconds
  int milliseconds = utc->time % 1000;
 
- tzset();
- time_t ltime = timegm(&utc_tm);
+ time_t ltime = mktime(&utc_tm);
+ ltime += -(utc_tm.tm_isdst * 3600) + (utc_tm.tm_gmtoff);
 
  struct tm local_tm = {0};
  localtime_r(&ltime, &local_tm);