epicsTime_localtime() currently reports daylight saving time incorrectly on Windows

[mdavidsaver]

Freddie Akeroyd reports:

I've noticed that the "tm_isdst" member of the "struct tm" returned by the Win32 implementation of epicsTime_localtime() is not currently reporting DST status correctly. The problem is that though the StandardDate / DaylightDate members of TIME_ZONE_INFORMATION are SYSTEMTIME structures, they have slightly different interpretations of their contents than usual in particular wDay == 5 means "last occurrence of wDayOfWeek in the month" rather than "5th day of month". One solution would be to use the status returned by GetTimeZoneInformation() which now seems to include the DST status, but I think the epicsTime_localtime() implementation could actually be replace by something simpler like (give or take a NULL pointer check):

     memcpy(pTM, localtime(pAnsiTime), sizeof(struct tm));

as on WIN32 the localtime() function uses thread local storage rather than global static storage (though the same TLS is shared with gmtime() )

http://www.aps.anl.gov/epics/tech-talk/2015/msg01646.php