target-i386: Fix addr16 prefix

target-i386: Fix addr16 prefix

While ADDSEG will only be false in 16-bit mode for LEA, it can be
false even in other cases when 16-bit addresses are obtained via
the 67h prefix in 32-bit mode.  In this case, gen_lea_v_seg forgets
to add a nonzero FS or GS base if CS/DS/ES/SS are all zero.  This
case is pretty rare but happens when booting Windows 95/98, and
this patch fixes it.

The bug is visible since commit d6a291498, but it was introduced
together with gen_lea_v_seg and it probably could be reproduced
with a "addr16 gs movsb" instruction as early as in commit
ca2f29f555805d07fb0b9ebfbbfc4e3656530977.

Reported-by: Hervé Poussineau <hpoussin@reactos.org>
Tested-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1456931078-21635-1-git-send-email-pbonzini@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>