Ref asm&global_asm from core::arch.

os/src/main.rs

@@ -1,7 +1,5 @@
 #![no_std]
 #![no_main]
-#![feature(global_asm)]
-#![feature(asm)]
 #![feature(panic_info_message)]
 #![feature(alloc_error_handler)]
 
@@ -10,6 +8,8 @@ extern crate alloc;
 #[macro_use]
 extern crate bitflags;
 
+use core::arch::global_asm;
+
 #[macro_use]
 mod console;
 mod lang_items;