vendor: update buildkit with typed errors support

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

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

@@ -23,7 +23,7 @@ import (
 	"runtime"
 )
 
-var unsupported = errors.New("extended attributes unsupported on " + runtime.GOOS)
+var errUnsupported = errors.New("extended attributes unsupported on " + runtime.GOOS)
 
 // Listxattr calls syscall listxattr and reads all content
 // and returns a string array
@@ -33,17 +33,17 @@ func Listxattr(path string) ([]string, error) {
 
 // Removexattr calls syscall removexattr
 func Removexattr(path string, attr string) (err error) {
-	return unsupported
+	return errUnsupported
 }
 
 // Setxattr calls syscall setxattr
 func Setxattr(path string, attr string, data []byte, flags int) (err error) {
-	return unsupported
+	return errUnsupported
 }
 
 // Getxattr calls syscall getxattr
 func Getxattr(path, attr string) ([]byte, error) {
-	return []byte{}, unsupported
+	return []byte{}, errUnsupported
 }
 
 // LListxattr lists xattrs, not following symlinks
@@ -53,12 +53,12 @@ func LListxattr(path string) ([]string, error) {
 
 // LRemovexattr removes an xattr, not following symlinks
 func LRemovexattr(path string, attr string) (err error) {
-	return unsupported
+	return errUnsupported
 }
 
 // LSetxattr sets an xattr, not following symlinks
 func LSetxattr(path string, attr string, data []byte, flags int) (err error) {
-	return unsupported
+	return errUnsupported
 }
 
 // LGetxattr gets an xattr, not following symlinks