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/posixmodule.c

@@ -9316,7 +9316,9 @@ os_dup_impl(PyObject *module, int fd)
     return _Py_dup(fd);
 }
 
-
+// dup2() is either provided by libc or dup2.c with AC_REPLACE_FUNCS().
+// dup2.c provides working dup2() if and only if F_DUPFD is available.
+#if (defined(HAVE_DUP3) || defined(F_DUPFD) || defined(MS_WINDOWS))
 /*[clinic input]
 os.dup2 -> int
     fd: int
@@ -9416,6 +9418,7 @@ os_dup2_impl(PyObject *module, int fd, int fd2, int inheritable)
 
     return res;
 }
+#endif
 
 
 #ifdef HAVE_LOCKF