ci: build.yml introduce riscv64 linux and freebsd

[eshattow]

Let's add riscv64 architecture builds to the workflow

Resolves: #2250

[eshattow]

Home Assistant depends on go2rtc docker image; I am developing a riscv64 build of Home Assistant and this is a blocker for me. Let's add riscv64 architecture builds to upstream go2rtc.

Tested on a fork of AlexxIT/go2rtc with some additional modifications to the workflow to ensure the docker image(s) jobs are not skipped, as expected it compiles and builds and publishes like the other supported go targets:

https://go.dev/wiki/FreeBSD

Kernel version, Architectures, Initial support version, Final support version
14-CURRENT, ...riscv64, ** ***,
13-STABLE, ...riscv64, ** ***,

https://go.dev/wiki/Linux

Architecture, Kernel version, Initial support version, Final support version
riscv, TBD, Go 1.14,

The table above refers to "riscv" however on actual hardware go env reports "riscv64":

# cat /sys/firmware/devicetree/base/{name,model} ; echo ; uname -a ; go env
Milk-V Mars CM Lite
Linux hay 6.19.11+deb14-riscv64 #1 SMP PREEMPT Debian 6.19.11-1 (2026-04-05) riscv64 GNU/Linux
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='riscv64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/es/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/es/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3100524024=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='riscv64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/es/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/es/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GORISCV64='rva20u64'
GOROOT='/usr/lib/go-1.24'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/es/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go-1.24/pkg/tool/linux_riscv64'
GOVCS=''
GOVERSION='go1.24.4'
GOWORK=''
PKG_CONFIG='pkg-config'

[eshattow]

I got confused about the base branch, this is correct now @AlexxIT ?

[skrashevich]

The same: #2251 (comment)

[eshattow]

The same: #2251 (comment)

Yes, rebased to AlexxIT/master

[eshattow]

ping @skrashevich the rebase is completed as requested, may I please get a review? thanks!