Update rtypes.py

Author: BobTheBuidler

mypyc/ir/rtypes.py

@@ -493,6 +493,9 @@ def __hash__(self) -> int:
 # Python range object.
 range_rprimitive: Final = RPrimitive("builtins.range", is_unboxed=False, is_refcounted=True)
 
+# Python weak reference object
+weakref_rprimitive: Final = RPrimitive("weakref.ReferenceType", is_unboxed=False, is_refcounted=True)
+
 
 def is_tagged(rtype: RType) -> bool:
     return rtype is int_rprimitive or rtype is short_int_rprimitive