Support RISC-V

[chazapis]

Buildroot already supports RISC-V, so it seems trivial to add this architecture to the list and move a step closer to RISC-V support for K3S.

I have already tested this manually, by running the scripts/ci script inside an Ubuntu 22.04 container with all necessary development tools. I also include the additional architecture in the Drone file.

[brandond]

We don't currently cross-build any of our architectures so this would be new. You've confirmed that the resulting artifacts function properly on a risc-v host?

[chazapis]

We don't currently cross-build any of our architectures so this would be new. You've confirmed that the resulting artifacts function properly on a risc-v host?

Sure. I have built k3s-root and k3s manually and tested them on a RISC-V QEMU VM running Ubuntu. This is some output to verify that the binaries are indeed usable:

root@ubuntu:~# uname -a
Linux ubuntu 5.19.0-1012-generic #13~22.04.1-Ubuntu SMP Thu Jan 12 15:34:31 UTC 2023 riscv64 riscv64 riscv64 GNU/Linux
root@ubuntu:~# cd /var/lib/rancher/k3s/data/current/bin
root@ubuntu:/var/lib/rancher/k3s/data/current/bin# file busybox
busybox: ELF 64-bit LSB executable, UCB RISC-V, double-float ABI, version 1 (SYSV), statically linked, stripped
root@ubuntu:/var/lib/rancher/k3s/data/current/bin# ./busybox id
uid=0(root) gid=0(root) groups=0(root)

[chazapis]

I have also submitted a relevant PR in k3s.