x/sys/unix: fix invalid syscall on linux/arm

Some system calls are obsolete and no longer available for EABI.
This CL replace such system call usages.

Updates golang/go#14524

Change-Id: Ib99b239455ca677e46d7097911904c45119051bd
Reviewed-on: https://go-review.googlesource.com/19945
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_amd64.go

@@ -86,6 +86,8 @@ func Time(t *Time_t) (tt Time_t, err error) {
 	return Time_t(tv.Sec), nil
 }
 
+//sys	Utime(path string, buf *Utimbuf) (err error)
+
 func TimespecToNsec(ts Timespec) int64 { return int64(ts.Sec)*1e9 + int64(ts.Nsec) }
 
 func NsecToTimespec(nsec int64) (ts Timespec) {