Try to work around check-fast breakage

Author: brson

src/test/run-pass/conditional-compile.rs

@@ -83,8 +83,8 @@ mod test_foreign_items {
     #[abi = "cdecl"]
     extern mod rustrt {
         #[cfg(bogus)]
-        fn rust_getcwd() -> *();
-        fn rust_getcwd() -> *();
+        fn rust_getcwd() -> ~str;
+        fn rust_getcwd() -> ~str;
     }
 }