Fix the signature of tp_new (#687)

According to the docs, the signature of `tp_new` should be:
`PyObject* tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)`
https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_new

We don't care about the arguments, but according to the C standard 6.3.2.3.8
this is undefined behavior:

> A pointer to a function of one type may be converted to a pointer to a
> function of another type and back again; the result shall compare equal to
> the original pointer. If a converted pointer is used to call a function whose
> type is not compatible with the pointed-to type, the behavior is undefined.

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf#page=60

In normal platforms the behavior is to work as expected, but in WebAssembly,
this crashes.

Fixes pyodide/pyodide#5015.

src/nb_internals.h

@@ -285,7 +285,7 @@ extern char *type_name(const std::type_info *t);
 
 // Forward declarations
 extern PyObject *inst_new_ext(PyTypeObject *tp, void *value);
-extern PyObject *inst_new_int(PyTypeObject *tp);
+extern PyObject *inst_new_int(PyTypeObject *tp, PyObject *args, PyObject *kwds);
 extern PyTypeObject *nb_static_property_tp() noexcept;
 extern type_data *nb_type_c2p(nb_internals *internals,
                               const std::type_info *type);

src/nb_type.cpp

@@ -65,7 +65,8 @@ static int inst_init(PyObject *self, PyObject *, PyObject *) {
 }
 
 /// Allocate memory for a nb_type instance with internal storage
-PyObject *inst_new_int(PyTypeObject *tp) {
+PyObject *inst_new_int(PyTypeObject *tp, PyObject * /* args */,
+                       PyObject * /*kwd */) {
     bool gc = PyType_HasFeature(tp, Py_TPFLAGS_HAVE_GC);
 
     nb_inst *self;
@@ -100,7 +101,6 @@ PyObject *inst_new_int(PyTypeObject *tp) {
     }
 
     return (PyObject *) self;
-
 }
 
 /// Allocate memory for a nb_type instance with external storage
@@ -1389,7 +1389,7 @@ static PyObject *nb_type_put_common(void *value, type_data *t, rv_policy rvp,
 
     nb_inst *inst;
     if (create_new)
-        inst = (nb_inst *) inst_new_int(t->type_py);
+        inst = (nb_inst *) inst_new_int(t->type_py, nullptr, nullptr);
     else
         inst = (nb_inst *) inst_new_ext(t->type_py, value);
 
@@ -1783,7 +1783,7 @@ void *nb_type_supplement(PyObject *t) noexcept {
 }
 
 PyObject *nb_inst_alloc(PyTypeObject *t) {
-    PyObject *result = inst_new_int(t);
+    PyObject *result = inst_new_int(t, nullptr, nullptr);
     if (!result)
         raise_python_error();
     return result;
@@ -1824,7 +1824,7 @@ void nb_inst_zero(PyObject *o) noexcept {
 }
 
 PyObject *nb_inst_alloc_zero(PyTypeObject *t) {
-    PyObject *result = inst_new_int(t);
+    PyObject *result = inst_new_int(t, nullptr, nullptr);
     if (!result)
         raise_python_error();
     nb_inst *nbi = (nb_inst *) result;