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/abstract.h

@@ -1,8 +1,7 @@
 #ifndef Py_ABSTRACTOBJECT_H
 #define Py_ABSTRACTOBJECT_H
-#ifdef __cplusplus
-extern "C" {
-#endif
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 #ifdef PY_SSIZE_T_CLEAN
 #define PyObject_CallFunction _PyObject_CallFunction_SizeT
@@ -1370,8 +1369,5 @@ PyAPI_FUNC(void) _Py_add_one_to_index_C(int nd, Py_ssize_t *index,
                                         const Py_ssize_t *shape);
 #endif /* !Py_LIMITED_API */
 
-
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* Py_ABSTRACTOBJECT_H */