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/pycapsule.h

@@ -1,3 +1,7 @@
+#ifndef Py_CAPSULE_H
+#define Py_CAPSULE_H
+COSMOPOLITAN_C_START_
+/* clang-format off */
 
 /* Capsule objects let you wrap a C "void *" pointer in a Python
    object.  They're a way of passing data through the Python interpreter
@@ -12,12 +16,6 @@
    documentation.
 */
 
-#ifndef Py_CAPSULE_H
-#define Py_CAPSULE_H
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 PyAPI_DATA(PyTypeObject) PyCapsule_Type;
 
 typedef void (*PyCapsule_Destructor)(PyObject *);
@@ -52,8 +50,5 @@ PyAPI_FUNC(void *) PyCapsule_Import(
     const char *name,           /* UTF-8 encoded string */
     int no_block);
 
-
-#ifdef __cplusplus
-}
-#endif
+COSMOPOLITAN_C_END_
 #endif /* !Py_CAPSULE_H */