target/s390x: Fix CLC corrupting cc_src

CLC updates cc_src before accessing the second operand; if the latter
is inaccessible, the former ends up containing a bogus value.

Fix by reading cc_src into a temporary first.

Fixes: 4f7403d5 ("target-s390: Convert CLC")
Closes: https://gitlab.com/qemu-project/qemu/-/issues/1865


Cc: qemu-stable@nongnu.org
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-ID: <20231106093605.1349201-2-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>