Update native support.

substrate/native-runtime/support/src/lib.rs

@@ -1,4 +1,8 @@
 pub use std::vec::Vec;
+pub use std::rc::Rc;
+pub use std::cell::RefCell;
+pub use std::boxed::Box;
+pub use std::mem::{size_of, transmute};
 
 pub fn storage(_key: &[u8]) -> Vec<u8> { vec![] }
 pub fn storage_into<T: Sized>(_key: &[u8]) -> Option<T> { None }