Fix windows breakage.

src/libcore/os.rs

@@ -554,12 +554,13 @@ pub fn make_dir(p: &Path, mode: c_int) -> bool {
 
     #[cfg(windows)]
     fn mkdir(p: &Path, _mode: c_int) -> bool {
+        use win32::*;
         // FIXME: turn mode into something useful? #2623
         do as_utf16_p(p.to_str()) |buf| {
             libc::CreateDirectoryW(buf, unsafe {
                 cast::reinterpret_cast(&0)
             })
-                != (0 as BOOL)
+                != (0 as libc::BOOL)
         }
     }