winpthreads: removed legacy time functions from pthread.h

Remove localtime_r from pthread.h which was a legacy hack for
compatibility with pthreads-win32. time.h is a more correct place for
localtime*, both for _POSIX compliance
<http://pubs.opengroup.org/onlinepubs/009695399/functions/localtime.html>
and MS for compatibility
<http://msdn.microsoft.com/en-us/library/bf12f0hc(v=vs.80).aspx>

Signed-off-by: Jonathan Yong <10walls@gmail.com>
localtime_r guard to _POSIX or _POSIX_THREAD_SAFE_FUNCTIONS

From http://www.unix.org/whitepapers/reentrant.html

"This is accomplished in the standard by associating the reentrancy
specifications with a separate option, {_POSIX_THREAD_SAFE_FUNCTIONS},
which is declared to be mandatory for implementations supporting the
threads option"

In pthread_unistd.h we define:

_POSIX_THREAD_SAFE_FUNCTIONS 200112L

Signed-off-by: Jonathan Yong <10walls@gmail.com>