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/Modules/atexitmodule.c

@@ -1,3 +1,4 @@
+/* clang-format off */
 /*
  *  atexit - allow programmer to define multiple exit functions to be executed
  *  upon normal program termination.
@@ -6,7 +7,7 @@
  +   Copyright 2007 Python Software Foundation.
  */
 
-#include "Python.h"
+#include "third_party/python/Include/Python.h"
 
 /* Forward declaration (for atexit_cleanup) */
 static PyObject *atexit_clear(PyObject*, PyObject*);