aes/asm/bsaes-x86_64.pl: fix Windows-specific bug in XTS.

#

# Core 2	9.83

# Nehalem	7.74

# Atom		18.9 (estimated, not measured yet)

# Atom		19.0

#

# November 2011.

#

#	const unsigned char iv[16]);

#

my ($twmask,$twres,$twtmp)=@XMM[13..15];

$arg6=~s/d$//;

$code.=<<___;

.globl	bsaes_xts_encrypt

.type	bsaes_xts_encrypt,\@abi-omnipotent