Adding explicit build-args for linux amd64

[jonathancross]

When attempting to build the latest firmware, the TARGETPLATFORM and TARGETARCH were not being automatically populated from the --platform linux/amd64 as assumed here:
https://github.com/BitBoxSwiss/bitbox02-firmware/blob/master/Dockerfile#L24

This lead to confusing errors late in the build process.

Docker indicates these AARGs are only set when using the buildkit backend: https://docs.docker.com/reference/dockerfile/#automatic-platform-args-in-the-global-scope

I'm using docker commandline, on PopOS.

In order to prevent issues for myself and other users, I am making this PR to explicitly set these parameters instead of relying on invisible buildkit magic.

[benma]

I assume you'd also need to change this then:

bitbox02-firmware/Makefile

Line 141 in 3096871

./scripts/container.sh build --pull --force-rm --no-cache -t shiftcrypto/firmware_v2:$(shell cat .containerversion) .

@NickeZ any idea why this is needed for @jonathancross while it seems to work fine for everyone else so far?

[jonathancross]

Please ignore. It turns out that my version of docker was old.