Converts a binary timestamp to a tm structure that expresses GMT
    or the equivalent UTC.

    Format

      #include <utc.h>

      int utc_gmtime(*timetm, *tns, *inacctm, *ins, *utc)

         struct tm *timetm;
         long *tns;
         struct tm *inacctm;
         long *ins;
         const utc_t *utc;