system: unbreak build for darwin

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
diff --git a/pkg/system/mknod_linux.go b/pkg/system/mknod_unix.go
similarity index 84%
rename from pkg/system/mknod_linux.go
rename to pkg/system/mknod_unix.go
index 5c65f8a..4586aad 100644
--- a/pkg/system/mknod_linux.go
+++ b/pkg/system/mknod_unix.go
@@ -1,3 +1,6 @@
+//go:build !freebsd && !windows
+// +build !freebsd,!windows
+
 package system // import "github.com/docker/docker/pkg/system"
 
 import (