work around incorrect C-API signature in PyPy3

Cython/Utility/Builtins.c

@@ -120,7 +120,7 @@ static PyObject* __Pyx_PyExec3(PyObject* o, PyObject* globals, PyObject* locals)
                 "code object passed to exec() may not contain free variables");
             goto bad;
         }
-        #if PY_VERSION_HEX < 0x030200B1
+        #if CYTHON_COMPILING_IN_PYPY || PY_VERSION_HEX < 0x030200B1
         result = PyEval_EvalCode((PyCodeObject *)o, globals, locals);
         #else
         result = PyEval_EvalCode(o, globals, locals);