*: Add promu build for darwin/arm64

[saswatamcode]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Helps with running binaries on apple silicon.
Should kick in from next release, but promu already supports it from v0.8.

Verification

[saswatamcode]

Hmm seems like it is broken, will take a look...

[yeya24]

Hmm seems like it is broken, will take a look...

Is it broken? I see build works.

[saswatamcode]

The check doesn't fail, but it just doesn't build,

> running the base builder docker image
github.com/prometheus/promu/cmd.runCrossbuild
	/home/runner/go/pkg/mod/github.com/prometheus/promu@v0.5.0/cmd/crossbuild.go:148
github.com/prometheus/promu/cmd.Execute
	/home/runner/go/pkg/mod/github.com/prometheus/promu@v0.5.0/cmd/promu.go:[13](https://github.com/thanos-io/thanos/actions/runs/6571719603/job/17851434842?pr=6824#step:5:14)0
main.main
	/home/runner/go/pkg/mod/github.com/prometheus/promu@v0.5.0/main.go:20
runtime.main
	/opt/hostedtoolcache/go/1.21.3/x64/src/runtime/proc.go:267
runtime.goexit
	/opt/hostedtoolcache/go/1.21.3/x64/src/runtime/asm_amd64.s:[16](https://github.com/thanos-io/thanos/actions/runs/6571719603/job/17851434842?pr=6824#step:5:17)50\n +  docker create -t --name promu-crossbuild-base1697703[17](https://github.com/thanos-io/thanos/actions/runs/6571719603/job/17851434842?pr=6824#step:5:18)5 quay.io/prometheus/golang-builder:1.[21](https://github.com/thanos-io/thanos/actions/runs/6571719603/job/17851434842?pr=6824#step:5:22)-base -i github.com/thanos-io/thanos -p linux/amd64 darwin/amd64 windows/amd64 freebsd/amd64 linux/arm64 linux/ppc64le

But figured out what needs to fix! 🙂

[saswatamcode]

And now promu breaks in different way. Looks like prometheus/promu#228
Will tackle this

[simonpasquier]

Discussed this offline: the build command breaks because it reinstalls the promu binary using go build ... while the GOOS and GOARCH environment variables are set to the target platform (e.g. darwin/amd64). Instead the promu installation command could set GOOS and GOARCH to GOHOSTOS and GOHOSTARCH variables respectively (doc).