Make warnings into errors

Author: varkor

src/test/ui/lint/no-unused-parens-return-block.rs

@@ -1,5 +1,8 @@
 // run-pass
 
+#![deny(unused_parens)]
+#![allow(unreachable_code)]
+
 fn main() {
     match (return) {} // ok
     if (return) {} // ok