Default console changes break Xen command-line

From David Woodhouse:

[Commit commit 1bec1cc0 ("ui/console: allow to override the default VC")] breaks the command line documented at https://qemu-project.gitlab.io/qemu/system/i386/xen.html

$ ./qemu-system-x86_64 --accel kvm,xen-version=0x40011,kernel-irqchip=split
-display none -chardev stdio,mux=on,id=char0,signal=off -mon char0
-device xen-console,chardev=char0 -drive file=${GUEST_IMAGE},if=xen

qemu-system-x86_64: cannot use stdio by multiple character devices qemu-system-x86_64: could not connect serial device to character backend 'stdio'

Can we make it create a Xen console by default, instead of a serial port? And/or make it not use stdio if something else on the command line already does?