Consolidate Linux readv implementation

This patch consolidates the readv Linux syscall implementation on
sysdeps/unix/sysv/linux/readv.c.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
arch64-linux-gnu, arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/readv.c: New file.

ChangeLog

@@ -1,5 +1,7 @@
 2016-05-10  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	* sysdeps/unix/sysv/linux/readv.c: New file.
+
 	* include/unistd.h (write): Add hidden proto.
 	* io/Makefile (CFLAGS-write.c): New define.
 	* nptl/Makefile (CFLAGS-write.c): Likewise.

sysdeps/unix/sysv/linux/readv.c

@@ -0,0 +1,27 @@
+/* Linux implementation for readv syscall.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+#include <sysdep-cancel.h>
+
+ssize_t
+__readv (int fd, const struct iovec *iov, int iovcnt)
+{
+  return SYSCALL_CANCEL (readv, fd, iov, iovcnt);
+}
+weak_alias (__readv, readv)