[macOS] Fix crashes due to the stabilization of the `!` (never) type (#428)
[macOS] Fix crashes due to the stabilization of the `!` (never) type (#428)

Due to the recent changes in the Rust compiler, unconstrained type
variables are now deduced to `!` instead of `()`. There are some
occurrences where `msg_send!` is used without constraining its return
type (relying on the assumption that they would be deduced to be `()`).
As a result, the macOS port of winit stopped working.

This PR fixes this issue (#426) by adding explicit return types to
such uses of `msg_send!`.
tomaka/winit