toolchain library fixes

[pat-s]

ref #256

WIP, currently testing.

Tested with

TARGETOS=linux TARGETARCH_XGO=arm64 TARGETARCH_BUILDX=linux/* make release-server-xgo

for both the arm64 and the amd64 image. Using aarch64-linux-gnu-gcc instead of arm-linux-gnueabi-gcc fails with an error so let's stick to arm-linux-gnueabi-gcc.

[pat-s]

I think some new tests would be good which test the cross-compile for all scenarios so errors can be spotted during a PR.

[pat-s]

OK so tests 5 & 7 were already broken before #255, so discarding them from the judgement of this PR (and commenting them out for the moment). (https://github.com/techknowlogick/xgo/actions/runs/11653506586/job/32445960620?pr=258)

[pat-s]

I also tried building @kolaente project but had issues during the frontend build. Without this, the xgo part errors due to missing deps. Hence I can't complete verify that the changes work, but the PATH issue not finding the compiler should be fixed.

[kolaente]

I've fixed the Vikunja test and commented out the other one in #259 - please rebase, then this should be good to go