Remove stime() function calls

Remove stime() function calls

stime() has been deprecated in glibc 2.31 and replaced with
clock_settime(). Let's replace the stime() function calls with
clock_settime() in preperation.

function                                             old     new   delta
rdate_main                                           197     224     +27
clock_settime                                          -      27     +27
date_main                                            926     941     +15
stime                                                 37       -     -37
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 2/0 up/down: 69/-37)             Total: 32 bytes

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>