unix: always use fstatat(AT_SYMLINK_NOFOLLOW) over lstat on AMD64

ARM64 does this exact same thing, and in fact this is required on
Android 9, where Bionic now only allows lstat on 32-bit platforms
Folks are running into this when using Android on Chromebooks,
which are keeping AMD64 Android alive. So, we change the AMD64
behavior to model that of ARM64.

Change-Id: Id933cc22b42ab365c12980915557bdbf88661a4d
Reviewed-on: https://go-review.googlesource.com/c/153319
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/syscall_linux_amd64.go

@@ -35,7 +35,11 @@ func InotifyInit() (fd int, err error) {
 //sys	Iopl(level int) (err error)
 //sys	Lchown(path string, uid int, gid int) (err error)
 //sys	Listen(s int, n int) (err error)
-//sys	Lstat(path string, stat *Stat_t) (err error)
+
+func Lstat(path string, stat *Stat_t) (err error) {
+	return Fstatat(AT_FDCWD, path, stat, AT_SYMLINK_NOFOLLOW)
+}
+
 //sys	Pause() (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

unix/zsyscall_linux_amd64.go

@@ -1862,21 +1862,6 @@ func Listen(s int, n int) (err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Lstat(path string, stat *Stat_t) (err error) {
-	var _p0 *byte
-	_p0, err = BytePtrFromString(path)
-	if err != nil {
-		return
-	}
-	_, _, e1 := Syscall(SYS_LSTAT, uintptr(unsafe.Pointer(_p0)), uintptr(unsafe.Pointer(stat)), 0)
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Pause() (err error) {
 	_, _, e1 := Syscall(SYS_PAUSE, 0, 0, 0)
 	if e1 != 0 {