test: fix the tests for windows

Author: erickt

src/test/compile-fail/deriving-primitive.rs

@@ -31,4 +31,4 @@ enum D { Baz { x: int } }
 //~^^ ERROR `FromPrimitive` cannot be derived for enums with struct variants
 //~^^^ ERROR `FromPrimitive` cannot be derived for enums with struct variants
 
-fn main() {}
+pub fn main() {}

src/test/run-pass/deriving-primitive.rs

@@ -19,7 +19,7 @@ enum A {
     Qux,
 }
 
-fn main() {
+pub fn main() {
     let x: Option<A> = FromPrimitive::from_int(int::max_value);
     assert_eq!(x, Some(Foo));