qemu-kvm: -no-reboot option broken in 12.x

When using the "-no-reboot" qemu option with kvm, qemu does nothing and immediately exits with no output or error message.   If I add the --no-kvm option to the command line, it works as expected.

It works fine in 11.0 and 11.1, but I tested all versions of 12.X, and they all have this problem.