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

Change-Id: I6145c915754f31e3c50f6a11568eb9d5ba12a778
GitHub-Last-Rev: 5b15f129cc
GitHub-Pull-Request: golang/sys#221
Reviewed-on: https://go-review.googlesource.com/c/sys/+/619255
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

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)

unix/zsyscall_linux.go

@@ -592,6 +592,16 @@ func ClockGettime(clockid int32, time *Timespec) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func ClockSettime(clockid int32, time *Timespec) (err error) {
+	_, _, e1 := Syscall(SYS_CLOCK_SETTIME, uintptr(clockid), uintptr(unsafe.Pointer(time)), 0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func ClockNanosleep(clockid int32, flags int, request *Timespec, remain *Timespec) (err error) {
 	_, _, e1 := Syscall6(SYS_CLOCK_NANOSLEEP, uintptr(clockid), uintptr(flags), uintptr(unsafe.Pointer(request)), uintptr(unsafe.Pointer(remain)), 0, 0)
 	if e1 != 0 {