booting a linux guest with qemu-system-sparc with icount enabled hangs

If you try to boot a Linux guest kernel on qemu-system-sparc with "-icount auto" it hangs just after printing "bootconsole [earlyprom0] disabled".

For example, if you download https://www.qemu-advent-calendar.org/2018/download/day11.tar.xz and extract the zImage.elf from it, you can boot it without icount and it will get to a login prompt:

  qemu-system-sparc -display none -vga none -machine SS-20 -serial stdio -kernel /tmp/day11/zImage.elf

But if you enable icount:

  qemu-system-sparc -icount auto -display none -vga none -machine SS-20 -serial stdio -kernel /tmp/day11/zImage.elf

the boot hangs, with the last message printed by the guest being "bootconsole [earlyprom0] disabled".

Tested with current head of git, commit a146af86.