Support Builds for ARM M1 Macs

[cfstras]

Summary

This PR adds build targets to the makefile to support building for darwin/arm64, which is the architecture for Apples processors going forward from the M1.

It also adds support for the arch in the get-chartmuseum script, which will then attempt to download the version. As soon as the first version with this build is released, everybody can enjoy it :)

Also added .PHONY labels to the other build-* targets, to prevent make confusion when files called build-* exist.

Testing

Successfully tested on an M1 MBP, macOS 11.5.2.

Caveat

Unfortunately, there is a cosmetic error message at the start coming from containerd, because it tries to call getCPUInfo() on every ARM arch:

ERRO[0000] failure getting variant                       error="getCPUInfo for OS darwin: not implemented"

See https://github.com/containerd/containerd/blob/v1.3.4/platforms/cpuinfo.go#L77-L93.

The bug is already fixed since 1.4.0 of containerd/containerd: containerd/containerd@7119a2a, but indirect dependencies still pull in old versions.

[scbizu]

Good job , could you pass the DCO verification ?

[cfstras]

@scbizu Should be good to go now :)

[scbizu]

The containerd dependency is from the helm dependency though ...

However , we can not bump our helm dependency to the latest version due to one potential break change .

And so , this PR may should be merged after we fixed the caveat ?

(After v0.14.0 , we need to deprecate the invalid semantic version by default and bump our Helm dependency to the latest and then we can also bump the containerd dependency to fix the caveat).

[cfstras]

I don't you need hold this back -- as mentioned, the error message is purely cosmetic, and has no implications on chartmuseum itself (apart from being slightly annoying).

Being able to build this on M1 with a weird log entry is better than not being able to run it at all ;)

[scbizu]

Sounds right , I can merge this in and it (the weird error message ) will disappear after we bump the containerd dependency , right ?

[cfstras]

Correct, that should be the case.

(noticed that the build failed though, it looks like helm does not live at https://storage.googleapis.com/kubernetes-helm/ anymore, but here: https://github.com/helm/helm/releases/tag/v2.17.0)

[scbizu]

Thank you , I will merge it and then fix the CI 😆