target-m68k: Do not cpu_abort on undefined insns

Report this properly via exception and, importantly, allow
the disassembler the chance to tell us what insn is not handled.
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NRichard Henderson <rth@twiddle.net>
Message-Id: <1478699171-10637-3-git-send-email-rth@twiddle.net>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

target/m68k/translate.c

@@ -1214,10 +1214,12 @@ DISAS_INSN(undef_fpu)
 
 DISAS_INSN(undef)
 {
-    M68kCPU *cpu = m68k_env_get_cpu(env);
-
+    /* ??? This is both instructions that are as yet unimplemented
+       for the 680x0 series, as well as those that are implemented
+       but actually illegal for CPU32 or pre-68020.  */
+    qemu_log_mask(LOG_UNIMP, "Illegal instruction: %04x @ %08x",
+                  insn, s->pc - 2);
     gen_exception(s, s->pc - 2, EXCP_UNSUPPORTED);
-    cpu_abort(CPU(cpu), "Illegal instruction: %04x @ %08x", insn, s->pc - 2);
 }
 
 DISAS_INSN(mulw)