[mypyc] Fix __call__ subclasses (#13152)

Fixes #12605 
Fixes mypyc/mypyc#925

Author: Fidget-Spinner

mypyc/codegen/emitclass.py

@@ -322,6 +322,10 @@ def emit_line() -> None:
         fields['tp_vectorcall_offset'] = 'offsetof({}, vectorcall)'.format(
             cl.struct_name(emitter.names))
         flags.append('_Py_TPFLAGS_HAVE_VECTORCALL')
+        if not fields.get('tp_vectorcall'):
+            # This is just a placeholder to please CPython. It will be
+            # overriden during setup.
+            fields['tp_call'] = 'PyVectorcall_Call'        
     fields['tp_flags'] = ' | '.join(flags)
 
     emitter.emit_line(f"static PyTypeObject {emitter.type_struct_name(cl)}_template_ = {{")

mypyc/test-data/run-classes.test

@@ -2206,3 +2206,13 @@ def test_serializable_sub_class_call_new() -> None:
     base: NonSerializable = sub
     with assertRaises(AttributeError):
         base.s
+
+[case testClassWithInherited__call__]
+class Base:
+    def __call__(self) -> int:
+        return 1
+
+class Derived(Base):
+    pass
+
+assert Derived()() == 1