tcg/i386: Check the size of instruction being translated

This fixes the bug: 'user-to-root privesc inside VM via bad translation
caching' reported by Jann Horn here:
https://bugs.chromium.org/p/project-zero/issues/detail?id=1122

Reviewed-by: Richard Henderson <rth@twiddle.net>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Message-Id: <20170323175851.14342-1-bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
static inline void gen_stack_update(DisasContext *s, int addend)
{
    gen_op_add_reg_im(mo_stacksize(s), R_ESP, addend);
}

static inline void gen_stack_update(DisasContext *s, int addend)
{
    gen_op_add_reg_im(mo_stacksize(s), R_ESP, addend);
}
