Introduce prototype-style function definitions for readv and writev.

Upstream, the old-style function definitions were removed in:

commit 42b7f5d48549b85386a9b28a1a90e66fd81ba273

Author: Joseph Myers <joseph@codesourcery.com>

Date:   Mon Oct 20 15:49:08 2014 +0000

    Move readv and writev definitions to syscalls.list (bug 14138).

diff --git a/sysdeps/unix/sysv/linux/readv.c b/sysdeps/unix/sysv/linux/readv.c

index e8acd65ce377963a..e49d54ede39d45af 100644

--- a/sysdeps/unix/sysv/linux/readv.c

+++ b/sysdeps/unix/sysv/linux/readv.c

@@ -39,10 +39,7 @@ static ssize_t __atomic_readv_replacement (int, const struct iovec *,

 ssize_t

-__libc_readv (fd, vector, count)

-     int fd;

-     const struct iovec *vector;

-     int count;

+__libc_readv (int fd, const struct iovec *vector, int count)

 {

   ssize_t result;

diff --git a/sysdeps/unix/sysv/linux/writev.c b/sysdeps/unix/sysv/linux/writev.c

index 8b018ecdf6fbc323..847a1057aa443238 100644

--- a/sysdeps/unix/sysv/linux/writev.c

+++ b/sysdeps/unix/sysv/linux/writev.c

@@ -38,10 +38,7 @@ static ssize_t __atomic_writev_replacement (int, const struct iovec *,

 ssize_t

-__libc_writev (fd, vector, count)

-     int fd;

-     const struct iovec *vector;

-     int count;

+__libc_writev (int fd, const struct iovec *vector, int count)

 {

   ssize_t result;