target/s390x: Fix DR/D INT64_MIN / -1 host crash

helper_divs32() divides the 64-bit dividend by the 32-bit divisor as a 64-bit
host operation, guarding only against a zero divisor. INT64_MIN / -1 therefore
overflows the host division before the representability check runs; on hosts
that trap this, QEMU is killed with SIGFPE instead of raising the
fixed-point-divide exception the guest expects:

    qemu-s390x: QEMU internal SIGFPE {code=INTDIV, addr=...}

helper_divs64() already guards the same case; add the missing check to
helper_divs32().

Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Fixes: b4e2bd3563af ("target-s390: Send signals for divide")
Cc: qemu-stable@nongnu.org
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260714190351.337923-2-iii@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>