message: Fixed the clock_gettime() unavailability
diff: // Copyright (C) 2018-2019 Hossein Moein
  // Distributed under the BSD Software License (see file License)
  -#include <time.h>
  #include "../include/DateTime.h"
  +#include <sys/time.h>
  // ----------------------------------------------------------------------------
  @@ -150,11 +150,11 @@ DateTime::DateTime (TIME_ZONE time_zone) throw () : time_zone_ (time_zone) {
  // set_time (mktime (&stm),
  // static_cast<MillisecondType>(syst.wMilliseconds));
  - set_time (::time (NULL), 0);
  -#else
  + set_time(::time(nullptr), 0);
  +#elifdef clock_gettime
  struct timespec ts;
  - ::clock_gettime (CLOCK_REALTIME, &ts);
  + ::clock_gettime(Clock_REALTIME, &ts);
  set_time(ts.tv_sec, 0);
  // This is a hack. Since the original resolution of DateTime was
  @@ -162,6 +162,12 @@ DateTime::DateTime (TIME_ZONE time_zone) throw () : time_zone_ (time_zone) {
  // convert to nanosecond manually here.
  //
  nanosecond_ = ts.tv_nsec;
  +#else
  + struct timeval tv { };
  +
  + ::gettimeofday(&tv, nullptr);
  + set_time(tv.tv_sec, tv.tv_usec);
  + nanosecond_ = 0;
  #endif // _WIN32
  }
  