target/m68k: Make semihosting system only

While we had a call to do_m68k_semihosting in linux-user, it
wasn't actually reachable.  We don't include DISAS_INSN(halt)
as an instruction unless system mode.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
3 files changed