Code review comment for lp:~epics-core/epics-base/tzwin32

These changes are reported to fix the issue. I've verified with cross-mingw/wine, which also needs to link against -lwinpthread. This change almost falls below the threshold were I wouldn't bother with a merge proposal, but as I don't do much work with win32 I'd like to get it checked/tested by someone who does.

http://www.aps.anl.gov/epics/tech-talk/2015/msg01660.php