gettime's gettimeofday call may fail

[Jim Meyering]

FYI,

I've just realized that gnulib's gettime function (currently
returning void) can fail, albeit under unusual circumstances.

On at least Solaris 9, gettimeofday is documented to fail like this:

     Additionally, the gettimeofday() function will fail for 32-bit
     interfaces if:

     EOVERFLOW
           The system time has progressed beyond 2038,  thus  the
           size  of  the  tv_sec  member of the timeval structure
           pointed to by tp is insufficient to hold  the  current
           time in seconds.

And something similar must happen on any system that has a
wider-than-32-bit clock counting seconds since the epoch, and that
also provides an environment where at least time_t is narrower.

Presuming that the same problem afflicts clock_gettime(3rt) or
that clock_gettime is not available for 32-bit time_t, then
gettime may return with *TS uninitialized.

At first I thought this meant we'd have to change gettime to
return an indication of success or failure.  However, I am now
inclined to leave it as is.  Anyone who sets the system clock past
2038 and then runs a gnulib-based program that they've compiled in
hamstrung-to-32-bit-time_t mode deserves whatever misbehavior they
provoke.

I figure that long before 2038 rolls around for real, everyone will
be using time_t that is sufficiently wide, so this won't be a problem.