target-i386: Fix jmp im on x86_64 when executing 32-bit code

When running grub-install (32-bit) on an x86_64 Linux system in qemu, it
hangs on a pagefault forever, because an integer overflow occurs on the
IP on "jmp im". This patch masks overflows for 32 bit IPs on a 64 bit
system, just like it is done for 16 bit IPs already.

Using this patch, x86_64 openSUSE installation works again.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Kevin Wolf <kwolf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5963 c046a42c-6fe2-441c-8c8c-71466251a162
