Fix omission of field names in printers of timeval structure

Fix omission of field names in printers of timeval structure

* print_time.c (time_fmt): Remove.
(timeval_fmt): New constant.
(print_timeval_t, sprint_timeval, print_timeval32_t, sprint_timeval32):
Use it instead of time_fmt.
* print_timex.c (print_timex): Print field names of the time field.
* printrusage.c (printrusage, printrusage32): Print field names
of ru_utime and ru_stime fields.
* tests/adjtimex.c (main): Add field names to expected output.
* tests/clock_nanosleep.c (main): Likewise.
* tests/futimesat.c (main): Likewise.
* tests/getrusage.c (main): Likewise.
* tests/nanosleep.c (main): Likewise.
* tests/oldselect.expected: Likewise.
* tests/utimes.c (main): Likewise.
* tests/wait4.c (sprint_rusage): Likewise.
* tests/waitid.c (sprint_rusage): Likewise.
* tests/xetitimer.c (main): Likewise.
* tests/xettimeofday.c (main): Likewise.
* tests/xselect.c (main): Likewise.