Use write_all() to write to write an entire string rather than write().

https://github.com/rust-lang-nursery/rust-clippy/wiki#unused_io_amount

cranelift/src/cton-util.rs

@@ -96,7 +96,7 @@ fn main() {
         if !msg.ends_with('\n') {
             msg.push('\n');
         }
-        io::stderr().write(msg.as_bytes()).unwrap();
+        io::stderr().write_all(msg.as_bytes()).unwrap();
         process::exit(1);
     }
 }