Add ARM toolchain support

[mikee47]

This PR addresses #2646 to support ARM systems such as Raspberry PI, Orange PI.

The Rp2040 toolchain version has been updated, and installs for appropriate machine architecture.

[mikee47]

Installing Rp2040 tools from repo does ensure maximum platform support, but as is typical lags behind current release somewhat.

I'm using a Raspberry PI 3 for testing, uname -a gives:

Linux rpi64 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr  3 17:24:16 BST 2023 aarch64 GNU/Linux

I'm getting GCC 8.3.1 installed, but current version (from October 2021) is 10.3 (see https://developer.arm.com/downloads/-/gnu-rm).

So will stick with the download approach.

[mikee47]

@laurentppol Are you able to give this a try? Ideally on a clean system, just to eliminate any potential issues.

[laurentppol]

@laurentppol Are you able to give this a try? Ideally on a clean system, just to eliminate any potential issues.

How? (what dirs to remove, how to install - as it is not yes merged)?

[mikee47]

@laurentppol Are you able to give this a try? Ideally on a clean system, just to eliminate any potential issues.

How? (what dirs to remove, how to install - as it is not yes merged)?

git fetch origin pull/2647/head:arm64-dev
git checkout arm64-dev

See https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally