x/build: gotip-freebsd-riscv64 builder is missing

[dmitshur]

There are currently no bots running at https://ci.chromium.org/ui/p/golang/builders/ci/gotip-freebsd-riscv64.

CC @mengzhuo, @golang/riscv64.

[mengzhuo]

Yes, I'm working on it, it's quite tricky.

Hardware issue:

• The old Hifive Unmatched can't be boot now due to EEPROM corrupted
• I had 4 Visionfive2, but FreeBSD has no ethernet support for them...(https://wiki.freebsd.org/riscv)
• Only 2 Sifive p550 can work for FreeBSD builder (Had to shared with Linux Megrez builder within kvm)

OS related issue:

1. FreeBSD 14 has dropped riscv64 pkg repo support which git/python311 can't be install by pkg, got to build by myself
2. cgo can't work riscv64: can't build on FreeBSD with cgo #73516

[gopherbot]

Change https://go.dev/cl/670595 mentions this issue: main.star: annotate missing riscv64 builders with tracking issues

[mengzhuo]

2 new builders has arrived.
I setup all FreeBSD riscv builders into the KVM based QEMU VM for better migrate consideration.

https://chromium-swarm.appspot.com/botlist?c=id&c=task&c=os&c=status&d=asc&f=cipd_platform%3Afreebsd-riscv64&k=cipd_platform&s=id

[gopherbot]

Change https://go.dev/cl/713560 mentions this issue: internal/releasetargets: update list for Go 1.26