py: Implement closures in native code generator.

Currently supports only x64 and Thumb2 archs.
diff --git a/py/nativeglue.c b/py/nativeglue.c
index 14638d4..674ee99 100644
--- a/py/nativeglue.c
+++ b/py/nativeglue.c
@@ -132,6 +132,8 @@
     mp_unpack_ex,
     mp_delete_name,
     mp_delete_global,
+    mp_obj_new_cell,
+    mp_make_closure_from_raw_code,
 };
 
 /*