Instead of creating GStrings and passing them into log_disas,
just print the annotations directly in tb_gen_code.

Fix the annotations for the slow paths of the TB, after the
part implementing the final guest instruction.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>