Fix LO_HI_LONG definition

The p{read,write}v{64} consolidation patch [1] added a wrong guard
for LO_HI_LONG definition.  It currently uses both
'__WORDSIZE == 64' and 'defined __ASSUME_WORDSIZE64_ILP32' to set
the value to be passed in one argument, otherwise it will be split
in two.

However it fails on MIPS64n32 where syscalls n32 uses the compat
implementation in the kernel meaning the off_t arguments are passed
in two separate registers.

GLIBC already defines a macro for such cases (__OFF_T_MATCHES_OFF64_T),
so this patch uses it instead.

Checked on x86_64, i686, x32, aarch64, armhf, and s390.

	* sysdeps/unix/sysv/linux/sysdep.h
	[__WORDSIZE == 64 || __ASSUME_WORDSIZE64_ILP32] (LO_HI_LONG): Remove
	guards.
	* misc/tst-preadvwritev-common.c: New file.
	* misc/tst-preadvwritev.c: Use tst-preadvwritev-common.c.
	* misc/tst-preadvwritev64.c: Use tst-preadwritev-common.c and add
	a check for files larger than 2GB.

[1] 4751bbe2