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_386.go

@@ -181,6 +181,8 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, err error) {
 //sysnb	Gettimeofday(tv *Timeval) (err error)
 //sysnb	Time(t *Time_t) (tt Time_t, err error)
 
+//sys	Utime(path string, buf *Utimbuf) (err error)
+
 // On x86 Linux, all the socket calls go through an extra indirection,
 // I think because the 5-register system call interface can't handle
 // the 6-argument calls like sendto and recvfrom.  Instead the