Makefile: add native build support for arm64 MacOS

[f1ko]

On MacOS uname -m returns arm64 whereas on Linux it returns aarch64.

Fixes #2257

[netlify]

✅ Deploy Preview for tetragon ready!

Name	Link
🔨 Latest commit	dd06d8a
🔍 Latest deploy log	https://app.netlify.com/sites/tetragon/deploys/6601ae92f90bf500080725e9
😎 Deploy Preview	https://deploy-preview-2258--tetragon.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[mtardy]

hey, I see that but I don't think you can build tetragon on macOS (because some pkg don't build on darwin) and we want to do that? Are you trying to cross build Linux Tetragon on macOS? If yes why don't you build on Linux directly?

[f1ko]

Essentially what is happening is that the Makefile is being evaluated on MacOS but the build itself can then happen elsewhere.
That is, for example, the case when using the make images target.
A Linux machine is required for using docker, so the actual build is happening on Linux anyways.
However, the target platform is being evaluated beforehand already while being on MacOS as make images is "natively" executed on the host.
By not being able to evaluate the target correctly on MacOS it falls back to creating an amd64 image which is later on not usable in kind running on the same arm64 machine.

Now an alternative may be to do everything on Linux immediately so that the target is rightfully evaluated when executing make images, however, it is a pain to do this setup for every repository that comes along.
For people working with the same small number of repositories all the time this is a one-time configuration that doesn't take too much effort to setup and doesn't need a lot of maintenance.
However, for someone that is constantly working with new repositories this is a pain to setup and to maintain in case of full disaster recovery automation.
One has to have enough space on the Linux VM, need to synchronise files back and forth between MacOS or maintain mounts, etc.

Therefore a common pattern on MacOS is to have a local lightweight Linux VM and exposing the docker socket to MacOS host so that one can "natively" use docker commands on MacOS.
Doing so results in a one-time setup that scales well regardless of projects that are being worked on and is therefore easier to automate and backup as well.

The proposed change does not break anything for existing users.
All it does is add support for a common workflow for MacOS development.

[mtardy]

yep okay why not! I'm thinking by the way that it would be a good change to write it with if/else statements:

ifeq ($(UNAME_M),x86_64)
	TARGET_ARCH ?= amd64
else ifeq ($(UNAME_M),aarch64)
	TARGET_ARCH ?= arm64
else ifeq ($(UNAME_M),arm64)
	TARGET_ARCH ?= arm64
else
	TARGET_ARCH ?= amd64
endif

[mtardy]

If that can help you, let's merge this!