syscall: use fchownat(2) in place of lchown(2) for linux/arm64

Fixes #11918

Replace calls to lchown(2) with fchownat(2) for linux/arm64 as the former is not suppored.

This change has also landed on the x/sys repo as CL 12837.

Change-Id: I58d4b144e051e36dd650ec9b7f3a02610ea943e5
Reviewed-on: https://go-review.googlesource.com/12833Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Russ Cox <rsc@golang.org>

src/syscall/syscall_linux_arm64.go

@@ -16,7 +16,6 @@ const _SYS_dup = SYS_DUP3
 //sysnb	Getgid() (gid int)
 //sysnb	Getrlimit(resource int, rlim *Rlimit) (err error)
 //sysnb	Getuid() (uid int)
-//sys	Lchown(path string, uid int, gid int) (err error)
 //sys	Listen(s int, n int) (err error)
 //sys	Pread(fd int, p []byte, offset int64) (n int, err error) = SYS_PREAD64
 //sys	Pwrite(fd int, p []byte, offset int64) (n int, err error) = SYS_PWRITE64
@@ -37,6 +36,10 @@ func Stat(path string, stat *Stat_t) (err error) {
 	return Fstatat(_AT_FDCWD, path, stat, 0)
 }
 
+func Lchown(path string, uid int, gid int) (err error) {
+	return Fchownat(_AT_FDCWD, path, uid, gid, _AT_SYMLINK_NOFOLLOW)
+}
+
 func Lstat(path string, stat *Stat_t) (err error) {
 	return Fstatat(_AT_FDCWD, path, stat, _AT_SYMLINK_NOFOLLOW)
 }

src/syscall/zsyscall_linux_arm64.go

@@ -1295,22 +1295,6 @@ func Getuid() (uid int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Lchown(path string, uid int, gid int) (err error) {
-	var _p0 *byte
-	_p0, err = BytePtrFromString(path)
-	if err != nil {
-		return
-	}
-	_, _, e1 := Syscall(SYS_LCHOWN, uintptr(unsafe.Pointer(_p0)), uintptr(uid), uintptr(gid))
-	use(unsafe.Pointer(_p0))
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Listen(s int, n int) (err error) {
 	_, _, e1 := Syscall(SYS_LISTEN, uintptr(s), uintptr(n), 0)
 	if e1 != 0 {