makefiles/boot/riotboot: pass BUILD_DIR to recursive Make call

[mguetschow]

Contribution description

riotboot for some reason resets the environment before a recursive make call. The new environment lacks BUILD_DIR.

Testing procedure

BUILD_DIR=test make -C tests/riotboot all fails on master with:

fatal: not a git repository: '.git'
fatal: not a git repository: '.git'
make[1]: *** [/home/mikolai/TUD/Code/RIOT/pkg/pkg.mk:132: /home/mikolai/TUD/Code/RIOT/build/pkg/cmsis/.pkg-state.git-downloaded] Error 128

With this change, it passes.

Issues/PRs references

Found while investigating #21438 (comment)

[crasbe]

riotboot for some reason resets the environment before a recursive make call.

This is understandable because the environment becomes very cluttered and there might be some flags that you don't want to set for the recursive call, but it is very difficult to filter them out individually.

What's a bit odd is that the code hasn't been touched in a long time, so why did this never show up? 🤔

[mguetschow]

What's a bit odd is that the code hasn't been touched in a long time, so why did this never show up? 🤔

I guess because few people know of and use BUILD_DIR :P

[maribu]

And also we never needed external packages in riotboot so far. But with mpaland-printf being used now with newlib, we started doing so now.

[riot-ci]

Murdock results

✔️ PASSED

625a8a8 makefiles/boot/riotboot: pass BUILD_DIR to recursive Make call

Success	Failures	Total	Runtime
1	0	1	02m:24s

Artifacts

• Documentation preview