gh-95174: Handle missing dup() and constants in WASI (GH-95229)

- check for ``dup()`` libc function
- handle missing ``F_DUPFD`` in ``dup2()`` replacement function
- add workaround for WASI libc bug in MSG_TRUNC
- ESHUTDOWN is missing, use EPIPE instead
- POLLPRI is missing, define as 0 (no-op)

Modules/errnomodule.c

@@ -280,6 +280,10 @@ errno_exec(PyObject *module)
 #ifdef ENOANO
     add_errcode("ENOANO", ENOANO, "No anode");
 #endif
+#if defined(__wasi__) && !defined(ESHUTDOWN)
+    // WASI SDK 16 does not have ESHUTDOWN, shutdown results in EPIPE.
+    #define ESHUTDOWN EPIPE
+#endif
 #ifdef ESHUTDOWN
     add_errcode("ESHUTDOWN", ESHUTDOWN, "Cannot send after transport endpoint shutdown");
 #else