Add conda based non-static bdw-gc support during compiler initialization

[kc611]

When trying to install spy using conda on macOS. I ran into problems with bwd-gc because the path for bwd-gc lives in the conda environment so cc couldn't find gc.h (nor -lgc at link time).

Steps I followed (in spy root directory):

conda create env -n spylang
conda activate spylang
pip install -e .
make -C spy/libspy

Hence I had to use the following fix so that bwd-gc could be detected. If it seems useful please do consider adding this fix to spy.

[antocuni]

thank your for investigating this.

So, from what I understand the problem is that libraries installed in a conda env are not automatically visible to the compiler, so we need to pass the right flags to locate it.

That's fine but it seems a more general fix for all conda-managed libraries, so probably we need to do it unconditionally, not only for gc.h.

But now my question is different: why does it work at all in linux then?
It's totally possible that it works by chance on my machine, and it picks up the system-installed libgc.

[paugier]

Did you try with Pixi (also conda based), which should officially be supported?

Note that we have in pyproject.toml

[tool.pixi.activation.env]
# to be able to link libgc (bdw-gc)
C_INCLUDE_PATH = "$PIXI_PROJECT_ROOT/.pixi/envs/default/include:$C_INCLUDE_PATH"
LIBRARY_PATH = "$PIXI_PROJECT_ROOT/.pixi/envs/default/lib:$LIBRARY_PATH"
# only useful for macOS
DYLD_LIBRARY_PATH = "$PIXI_PROJECT_ROOT/.pixi/envs/default/lib:$DYLD_LIBRARY_PATH"

[antocuni]

(for reference, Kaustubh is an Anaconda colleague and we hit this problem when I was trying to onboard him).

Did you try with Pixi (also conda based), which should officially be supported?

@paugier that was also my first reaction: we test pixi, why it doesn't work?
It turns out that at least on mac, this doesn't seem to work; this happens on both my Mac and @kc611 Mac (using pixi):

❯ spy build -x examples/hello.spy
[debug] examples/build/hello
dyld[77840]: Library not loaded: @rpath/libgc.1.dylib
  Referenced from: <0BAAF8DB-04AA-3A4B-BB13-997425F753F5> /Users/antocuni/anaconda/spy/examples/build/hello
  Reason: no LC_RPATH's found

What I haven't understood is whether this is a mac-specific problem, or it's also a linux problem which for some reason it's not triggered.
Do we test build -x in pixi tests?