QEMU 4.1 and RISC-V

[Li-Wen Hsu]

I found that RISC-V test started failing recently:
https://ci.freebsd.org/job/FreeBSD-head-riscv64-test/

After some checking, I found the issue is our bbl image cannot boot
with this command:

qemu-system-riscv64 -nographic -m 2048M -kernel ./bbl

in QEMU 4.1, while 3.1 and 4.0 are fine.  I've switched the QEMU
version used in that job to 4.0, but I think it would be best if we
can find the root cause is in FreeBSD or QEMU.

Can anyone also help on this?

Thanks,
Li-Wen