Fix FreeBSD compilation

Corrects compile on FreeBSD by handling the lack of ENODATA on FreeBSD.
Since continuity project has already handled this, using their const is
simpler than separating a few extra files in containerd/containerd.

Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>

archive/tar_unix.go

@@ -123,7 +123,7 @@ func handleLChmod(hdr *tar.Header, path string, hdrInfo os.FileInfo) error {
 
 func getxattr(path, attr string) ([]byte, error) {
 	b, err := sysx.LGetxattr(path, attr)
-	if err == unix.ENOTSUP || err == unix.ENODATA {
+	if err == unix.ENOTSUP || err == sysx.ENODATA {
 		return nil, nil
 	}
 	return b, err