unix: use Fstatat for Stat on linux/amd64

The stat syscall is disallowed by Android's seccomp policy on
linux/amd64. Use the fstatat syscall with AT_FDCWD and zero flags to
achieve the same behavior.

CL 109835 did the same for package syscall.

Change-Id: Iaa7d0dbf17ade4803f59b4361973ce627bcb65b4
Reviewed-on: https://go-review.googlesource.com/110061
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_amd64.go

diff --git a/unix/syscall_linux_amd64.go b/unix/syscall_linux_amd64.go
index 86a7393..d121106 100644
--- a/unix/syscall_linux_amd64.go
+++ b/unix/syscall_linux_amd64.go
@@ -48,7 +48,12 @@
 //sysnb	Setreuid(ruid int, euid int) (err error)
 //sys	Shutdown(fd int, how int) (err error)
 //sys	Splice(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int64, err error)
-//sys	Stat(path string, stat *Stat_t) (err error)
+
+func Stat(path string, stat *Stat_t) (err error) {
+	// Use fstatat, because Android's seccomp policy blocks stat.
+	return Fstatat(AT_FDCWD, path, stat, 0)
+}
+
 //sys	Statfs(path string, buf *Statfs_t) (err error)
 //sys	SyncFileRange(fd int, off int64, n int64, flags int) (err error)
 //sys	Truncate(path string, length int64) (err error)

unix/zsyscall_linux_amd64.go

diff --git a/unix/zsyscall_linux_amd64.go b/unix/zsyscall_linux_amd64.go
index 02e45b4..33c02b2 100644
--- a/unix/zsyscall_linux_amd64.go
+++ b/unix/zsyscall_linux_amd64.go
@@ -1897,21 +1897,6 @@
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Stat(path string, stat *Stat_t) (err error) {
-	var _p0 *byte
-	_p0, err = BytePtrFromString(path)
-	if err != nil {
-		return
-	}
-	_, _, e1 := Syscall(SYS_STAT, 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 Statfs(path string, buf *Statfs_t) (err error) {
 	var _p0 *byte
 	_p0, err = BytePtrFromString(path)