`make check-stage1` failed

[edwardw]

With error:

rust/src/librustuv/lib.rs:43:25: 43:42 error: unknown feature, #[deny(unknown_features)] on by default

But make rustc-stage1 runs smoothly. Weird. Repository head 0ae4b97.

[tomjakubowski]

seeing this on the travis build for #15071

[alexcrichton]

Closing, this is just a stage0/snapshot issue. This will be resolved once we have a new snapshot (one is building now).