Make main public to accommodate check-fast

Author: nikomatsakis

src/test/run-pass/regions-variance-contravariant-use-contravariant.rs

@@ -29,4 +29,4 @@ fn use_<'a>(c: Contravariant<'a>) {
     fn collapse<'b>(x: &'b int, c: Contravariant<'b>) { }
 }
 
-fn main() {}
+pub fn main() {}

src/test/run-pass/regions-variance-covariant-use-covariant.rs

@@ -26,4 +26,4 @@ fn use_<'a>(c: Covariant<'a>) {
     let _: Covariant<'static> = c;
 }
 
-fn main() {}
+pub fn main() {}