* misc/Makefile (routines): Add preadv, preadv64, pwritev, pwritev64.

* misc/Makefile (routines): Add preadv, preadv64, pwritev, pwritev64.

	* misc/Versions: Export preadv, preadv64, pwritev, pwritev64 for
	GLIBC_2.10.
	* misc/sys/uio.h: Declare preadv, preadv64, pwritev, pwritev64.
	* sysdeps/unix/sysv/linux/kernel-features.h: Add entries for preadv
	and pwritev.
	* misc/preadv.c: New file.
	* misc/preadv64.c: New file.
	* misc/pwritev.c: New file.
	* misc/pwritev64.c: New file.
	* sysdeps/posx/preadv.c: New file.
	* sysdeps/posx/preadv64.c: New file.
	* sysdeps/posx/pwritev.c: New file.
	* sysdeps/posx/pwritev64.c: New file.
	* sysdeps/unix/sysv/linux/preadv.c: New file.
	* sysdeps/unix/sysv/linux/preadv64.c: New file.
	* sysdeps/unix/sysv/linux/pwritev.c: New file.
	* sysdeps/unix/sysv/linux/pwritev64.c: New file.
	* sysdeps/unix/sysv/linux/wordsize-64/preadv64.c: New file.
	* sysdeps/unix/sysv/linux/wordsize-64/pwritev64.c: New file.