unix: add ClockSettime on Linux

The syscall clock_settime(3) is used to set the time on the specified
clock.  It is a counterpart to clock_gettime(3) which is already
exposed as ClockGettime here.

Fixes golang/go#69830

Author: yarikk

unix/syscall_linux.go

@@ -1860,6 +1860,7 @@ func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 //sys	ClockAdjtime(clockid int32, buf *Timex) (state int, err error)
 //sys	ClockGetres(clockid int32, res *Timespec) (err error)
 //sys	ClockGettime(clockid int32, time *Timespec) (err error)
+//sys	ClockSettime(clockid int32, time *Timespec) (err error)
 //sys	ClockNanosleep(clockid int32, flags int, request *Timespec, remain *Timespec) (err error)
 //sys	Close(fd int) (err error)
 //sys	CloseRange(first uint, last uint, flags uint) (err error)