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/errcode.h

@@ -1,8 +1,7 @@
 #ifndef Py_ERRCODE_H
 #define Py_ERRCODE_H
-#ifdef __cplusplus
-extern "C" {
-#endif
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 
 /* Error codes passed around between file input, tokenizer, parser and
@@ -32,7 +31,5 @@ extern "C" {
 #define E_IDENTIFIER    26      /* Invalid characters in identifier */
 #define E_BADSINGLE	27	/* Ill-formed single statement input */
 
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_ERRCODE_H */