target/s390x: Use tcg_constant_* for DisasCompare

target/s390x: Use tcg_constant_* for DisasCompare

The a and b fields are not modified by the consumer,
and while we need not free a constant, tcg will quietly
ignore such frees, so free_compare need not be changed.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230220184052.163465-3-richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>