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>
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)