du: count reflink disk usage only once

Author: aaron-ang

Cargo.lock

@@ -30,6 +30,7 @@ uucore = { workspace = true, features = [
 ] }
 thiserror = { workspace = true }
 fluent = { workspace = true }
+libc = { workspace = true }
 
 [target.'cfg(all(unix, not(target_os = "redox")))'.dependencies]
 uucore = { workspace = true, features = ["safe-traversal"] }