Remove pkgconf spkg

[dimpase]

pkgconf, a.k.a. pkg-config, is available on all systems we support - even on the "naked" (no homebrew/macports) macOS one can install a formally certified/notarised package https://github.com/donmccaughey/pkg-config_pkg - so there is no reason to keep it in the tree.

There are big advantages to have pkg-config available at configure time, as recognition of several crucial external spkgs, such as (open)blas, zlib, etc. hinges upon pkg-config.
With this PR in, we proceed to remove them.

Last but not the least, it simplifies the Makefile by getting rid of base target, which becomes empty

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

• remove bzip2 spkg #40011 - remove bzip2 spkg.
• update planaritry to 4.0.0.0 #40153 - planarity spkg fix (can't build otherwise)

[github-actions]

Documentation preview for this PR (built with commit f48be88; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[tobiasdiez]

CI runs for full coverage:
https://github.com/dimpase/sage/actions/runs/15432603560
https://github.com/dimpase/sage/actions/runs/15432607148

[tobiasdiez]

CI is green, so this looks good to me.

It looks like there are some unrelated changes here in planarity, or are these coming from another dependency PR?

[dimpase]

right, the planarity thing comes from the fact that I cannot build Sage without it - it's from a positively reviewed PR #40153 which should be in the coming beta. I forgot to list it in the deps, done now.

[dimpase]

fixed a typo leading to docbuild - should be OK now (it builds locally)

[tobiasdiez]

Small nitpick: the CI https://github.com/sagemath/sage/actions/runs/15716873483/job/44288781941?pr=40204#step:11:497 complains about

real_configure: WARNING: unrecognized options: --with-system-bzip2, --with-system-pkgconf

I think these flags come from

sage/.ci/write-dockerfile.sh

Line 50 in 11baeed

SYSTEM_CONFIGURE_ARGS+=" --with-system-${SPKG}=${WITH_SYSTEM_SPKG}"

If this is something that could be fixed easily, I would prefer if its done as part of this PR - if not, also no biggy.

[dimpase]

@tobiasdiez are these not coming from a previous generation of a docker image, and would go away in the next beta?

I tried to see where ${SPKG}, in the line you point at, would come from, and just don't find pkgconf anywhere suspected.

[tobiasdiez]

Sounds reasonable. It's sad that you cannot really trust the CI 🙄.

Thanks for checking though!