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/sysmodule.h

@@ -1,11 +1,7 @@
-
-/* System module interface */
-
 #ifndef Py_SYSMODULE_H
 #define Py_SYSMODULE_H
-#ifdef __cplusplus
-extern "C" {
-#endif
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 PyAPI_FUNC(PyObject *) PySys_GetObject(const char *);
 PyAPI_FUNC(int) PySys_SetObject(const char *, PyObject *);
@@ -37,7 +33,5 @@ PyAPI_FUNC(PyObject *) PySys_GetXOptions(void);
 PyAPI_FUNC(size_t) _PySys_GetSizeOf(PyObject *);
 #endif
 
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_SYSMODULE_H */