use UFCS in #[deriving(Hash)]

expansion now uses `::std:#️⃣:Hash::hash(&*__self_0_0, __arg_0)` instead of
`(*__self_0_0).hash(__arg_0)`

closes #21160

src/libstd/io/process.rs

@@ -21,6 +21,8 @@ use prelude::v1::*;
 use collections::HashMap;
 use ffi::CString;
 use fmt;
+// NOTE(stage0) remove import after a snapshot
+#[cfg(stage0)]
 use hash::Hash;
 use io::pipe::{PipeStream, PipePair};
 use io::{IoResult, IoError};