Perform build and magnum tuning

Building o//third_party/python now takes 5 seconds on my PC

This change works towards modifying Python to use runtime dispatching
when appropriate. For example, when loading the magnums in the socket
module, it's a good idea to check if the magnum is zero, because that
means the local system platform doesn't support it.

third_party/python/Objects/clinic/dictobject.inc

@@ -0,0 +1,43 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(dict_fromkeys__doc__,
+"fromkeys($type, iterable, value=None, /)\n"
+"--\n"
+"\n"
+"Returns a new dict with keys from iterable and values equal to value.");
+
+#define DICT_FROMKEYS_METHODDEF    \
+    {"fromkeys", (PyCFunction)dict_fromkeys, METH_VARARGS|METH_CLASS, dict_fromkeys__doc__},
+
+static PyObject *
+dict_fromkeys_impl(PyTypeObject *type, PyObject *iterable, PyObject *value);
+
+static PyObject *
+dict_fromkeys(PyTypeObject *type, PyObject *args)
+{
+    PyObject *return_value = NULL;
+    PyObject *iterable;
+    PyObject *value = Py_None;
+
+    if (!PyArg_UnpackTuple(args, "fromkeys",
+        1, 2,
+        &iterable, &value)) {
+        goto exit;
+    }
+    return_value = dict_fromkeys_impl(type, iterable, value);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(dict___contains____doc__,
+"__contains__($self, key, /)\n"
+"--\n"
+"\n"
+"True if D has a key k, else False.");
+
+#define DICT___CONTAINS___METHODDEF    \
+    {"__contains__", (PyCFunction)dict___contains__, METH_O|METH_COEXIST, dict___contains____doc__},
+/*[clinic end generated code: output=926326109e3d9839 input=a9049054013a1b77]*/