vendor: update buildkit to 539be170

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/containerd/continuity/AUTHORS

@@ -12,8 +12,11 @@ Darren Stahl <darst@microsoft.com>
 Derek McGowan <derek@mcg.dev>
 Derek McGowan <derek@mcgstyle.net>
 Edward Pilatowicz <edward.pilatowicz@oracle.com>
+Fu Wei <fuweid89@gmail.com>
+Hajime Tazaki <thehajime@gmail.com>
 Ian Campbell <ijc@docker.com>
 Ivan Markin <sw@nogoegst.net>
+Jacob Blain Christen <jacob@rancher.com>
 Justin Cormack <justin.cormack@docker.com>
 Justin Cummins <sul3n3t@gmail.com>
 Kasper Fabæch Brandt <poizan@poizan.dk>
@@ -23,10 +26,11 @@ Michael Crosby <michael@thepasture.io>
 Michael Wan <zirenwan@gmail.com>
 Mike Brown <brownwm@us.ibm.com>
 Niels de Vos <ndevos@redhat.com>
+Phil Estes <estesp@amazon.com>
 Phil Estes <estesp@gmail.com>
 Phil Estes <estesp@linux.vnet.ibm.com>
-Samuel Karp <me@samuelkarp.com>
 Sam Whited <sam@samwhited.com>
+Samuel Karp <me@samuelkarp.com>
 Sebastiaan van Stijn <github@gone.nl>
 Shengjing Zhu <zhsj@debian.org>
 Stephen J Day <stephen.day@docker.com>

vendor/github.com/containerd/continuity/sysx/nodata_unix.go

@@ -1,3 +1,4 @@
+//go:build darwin || freebsd || openbsd
 // +build darwin freebsd openbsd
 
 /*

vendor/github.com/containerd/continuity/sysx/xattr.go

@@ -1,3 +1,4 @@
+//go:build linux || darwin
 // +build linux darwin
 
 /*

vendor/github.com/containerd/continuity/sysx/xattr_unsupported.go

@@ -1,3 +1,4 @@
+//go:build !linux && !darwin
 // +build !linux,!darwin
 
 /*