x86-64: Update LO_HI_LONG for p{readv,writev}{64}v2

x86-64: Update LO_HI_LONG for p{readv,writev}{64}v2

The kernel interface for p{readv,writev}{64}v is

(unsigned long fd, {const }struct iovec *iov, unsigned long vlen,
 unsigned long pos_l, unsigned long pos_h)

Except for targets which define __ARCH_WANT_COMPAT_SYS_PREADV64 and
__ARCH_WANT_COMPAT_SYS_PWRITEV64,

(unsigned long fd, {const }struct iovec *iov, unsigned long vlen,
 off64_t pos)

is used for p{readv,writev}{64}v.  X32 is the only such target.  The
LO_HI_LONG macro is used to pass offset to the pos_l and pos_h pair.
Since pos_h is ignored when size of offset == sizeof of pos_l, x86-64
has

 #define LO_HI_LONG(val) (val)

But the kernel interface for p{readv,writev}{64}v2 is

(unsigned long fd, {const }struct iovec *iov, unsigned long vlen,
 unsigned long pos_l, unsigned long pos_h, int flags)

Except for targets which define __ARCH_WANT_COMPAT_SYS_PREADV64V2 and
__ARCH_WANT_COMPAT_SYS_PWRITEV64V2,

(unsigned long fd, {const }struct iovec *iov, unsigned long vlen,
 off64_t pos, int flags)

is used for p{readv,writev}{64}v2.  X32 is the only such target.  Update
x86-64 LO_HI_LONG to pass 0 as the high part of the offset argument for
p{readv,writev}{64}v2 and define a different LO_HI_LONG for x32 to only
pass one argument for offset.

Tested on x32 and x86-64.

	* sysdeps/unix/sysv/linux/x86_64/sysdep.h (LO_HI_LONG): Pass
	0 as the high part of offset.
	* sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h (LO_HI_LONG): New.