Use ctypes in native function declarations

src/libstd/test.rs

@@ -5,6 +5,7 @@
 
 import result::{ok, err};
 import io::writer_util;
+import core::ctypes;
 
 export test_name;
 export test_fn;
@@ -28,7 +29,7 @@ export joinable;
 
 #[abi = "cdecl"]
 native mod rustrt {
-    fn sched_threads() -> uint;
+    fn sched_threads() -> ctypes::size_t;
 }
 
 // The name of a test. By convention this follows the rules for rust