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/parsetok.h

@@ -1,11 +1,8 @@
-
-/* Parser-tokenizer link interface */
 #ifndef Py_LIMITED_API
 #ifndef Py_PARSETOK_H
 #define Py_PARSETOK_H
-#ifdef __cplusplus
-extern "C" {
-#endif
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 typedef struct {
     int error;
@@ -101,8 +98,6 @@ PyAPI_FUNC(node *) PyParser_ParseStringObject(
 PyAPI_FUNC(void) PyParser_SetError(perrdetail *);
 PyAPI_FUNC(void) PyParser_ClearError(perrdetail *);
 
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_PARSETOK_H */
 #endif /* !Py_LIMITED_API */