docker: Add support for Linux arm64 docker builds

[redsh4de]

Modifies Dockerfile.linux and Makefile to allow users to compile static arm64 linux builds.

For arm64 builds, an extra optional argument --build--arg UBUNTU_VERSION=18.04 will need to be added to the docker build command. Running make with docker run, release-static would have to be changed to release-static-linux-armv8.

[selsta]

Could you also add instructions to readme?

[redsh4de]

Updated :)

[selsta]

Thanks, do you know how to squash your commits?

[redsh4de]

Haven't done it before, would git rebase -i HEAD~4 be the way to go about it in our case?

[selsta]

I usually do:

git rebase -i origin/master

and then I set the commits that I want to squash to s.

Edit: what you wrote should work too, I just noticed that you are in master branch so what I wrote doesn't apply.

[redsh4de]

That takes care of that :D

[selsta]

@zer0conf something went wrong

[redsh4de]

Fixed, the squash reached a bit too far back

[selsta]

Some unintended commits got added again, I think the issue is that you opened this from master branch. Will try to get this merged after the v0.18 release.

[redsh4de]

Checked why docker-linux-static failed, stems from an error while cloning m4:
fatal: Could not parse object 'f662e3a93ebdec3d1c9374382dcc070093a42fed'.

[selsta]

yea i fixed it here #3969