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/sliceobject.c

@@ -1,3 +1,7 @@
+/* clang-format off */
+#include "third_party/python/Include/Python.h"
+#include "third_party/python/Include/structmember.h"
+
 /*
 Written by Jim Hugunin and Chris Chase.
 
@@ -13,9 +17,6 @@ the Py_NoneStruct in that there is no way to create other objects of
 this type and there is exactly one in existence.
 */
 
-#include "Python.h"
-#include "structmember.h"
-
 static PyObject *
 ellipsis_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
 {