As preadv and pwritev accept off_t type the prototypes should be declared as follows

extern ssize_t preadv (int __fd, const struct iovec *__iovec, int __count,
                       off_t __offset) __wur;
                                                                              
extern ssize_t pwritev (int __fd, const struct iovec *__iovec, int __count,
                        off_t __offset) __wur;

to take into account _FILE_OFFSET_BITS=64 define.

I am not sure but probably it is better to redeclare these prototypes
by analogy with sendfile using __REDIRECT_NTH.