libstd: convert `Duration` unops to by value

src/libstd/time/duration.rs

@@ -265,6 +265,8 @@ pub fn is_zero(&self) -> bool {
     }
 }
 
+// NOTE(stage0): Remove impl after a snapshot
+#[cfg(stage0)]
 impl Neg<Duration> for Duration {
     #[inline]
     fn neg(&self) -> Duration {
@@ -276,6 +278,18 @@ fn neg(&self) -> Duration {
     }
 }
 
+#[cfg(not(stage0))]  // NOTE(stage0): Remove cfg after a snapshot
+impl Neg<Duration> for Duration {
+    #[inline]
+    fn neg(self) -> Duration {
+        if self.nanos == 0 {
+            Duration { secs: -self.secs, nanos: 0 }
+        } else {
+            Duration { secs: -self.secs - 1, nanos: NANOS_PER_SEC - self.nanos }
+        }
+    }
+}
+
 // NOTE(stage0): Remove impl after a snapshot
 #[cfg(stage0)]
 impl Add<Duration,Duration> for Duration {