linux-user/s390x: signal with SIGFPE on compare-and-trap

linux-user/s390x: signal with SIGFPE on compare-and-trap

Currently when a compare-and-trap instruction is executed, qemu will
always raise a SIGILL signal. On real hardware, a SIGFPE is raised.

Change the PGM_DATA case in cpu_loop to follow the behavior in
linux kernel /arch/s390/kernel/traps.c.
 * Only raise SIGILL if DXC == 0
 * If DXC matches a non-simulated IEEE exception, raise SIGFPE with
   correct si_code
 * Raise SIGFPE with si_code == 0 for everything else

When applied on 20210705210434.45824-2-iii@linux.ibm.com, this fixes
crashes in the java jdk such as the linked bug.

Signed-off-by: Jonathan Albrecht <jonathan.albrecht@linux.vnet.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Buglink: https://bugs.launchpad.net/qemu/+bug/1920913
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/319
Message-Id: <20210709160459.4962-2-jonathan.albrecht@linux.vnet.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>