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/pydebug.h

@@ -1,9 +1,8 @@
 #ifndef Py_LIMITED_API
 #ifndef Py_PYDEBUG_H
 #define Py_PYDEBUG_H
-#ifdef __cplusplus
-extern "C" {
-#endif
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 /* These global variable are defined in pylifecycle.c */
 /* XXX (ncoghlan): move these declarations to pylifecycle.h? */
@@ -33,8 +32,6 @@ PyAPI_DATA(int) Py_LegacyWindowsStdioFlag;
    PYTHONPATH and PYTHONHOME from the environment */
 #define Py_GETENV(s) (Py_IgnoreEnvironmentFlag ? NULL : getenv(s))
 
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_PYDEBUG_H */
 #endif /* Py_LIMITED_API */