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/Include/dictobject.h

@@ -1,9 +1,7 @@
 #ifndef Py_DICTOBJECT_H
 #define Py_DICTOBJECT_H
-#ifdef __cplusplus
-extern "C" {
-#endif
-
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 /* Dictionary object type -- mapping from hashable object to object */
 
@@ -171,7 +169,5 @@ int _PyObjectDict_SetItem(PyTypeObject *tp, PyObject **dictptr, PyObject *name,
 PyObject *_PyDict_LoadGlobal(PyDictObject *, PyDictObject *, PyObject *);
 #endif
 
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_DICTOBJECT_H */