Allow building with CMake 4.0 and use GNUInstalldirs

[LecrisUT]

Pull Request Notice

Before sending a pull request make sure each commit solves one clear, minimal,
plausible problem. Further each commit should have the following format:

Problem: X is broken

Solution: do Y and Z to fix X

Is this really a strict requirement? Some of the commits are basically common CMake standards with no clear defined problem. Would make sense maybe when squashing the PR and writing an appropriate message in the PR description to be used.

Problem: Project does not build with CMake 4.0 and many patterns are outdated

Solution: Bump the CMake policies to use the latest policies up to 4.0 and use more modern CMake patterns in some places

[LecrisUT]

Since the CI is broken (beyond what bumping the builder to ubuntu-latest), here are the builds running on Fedora rawhide (linked inside are the builds running for CMake 4.0)

[bluca]

As the header in these files mention, these files are generated, so these changes have to happen in https://github.com/zeromq/zproject or they'll be overwritten on the next regeneration

[LecrisUT]

Transferred over at zeromq/zproject#1345. I couldn't follow the generation instructions there, so I am asking for help on that front, or I would do that generation manually as well.

[sphaero]

Since it is in zproject now are you able to regenerate and send a new PR for this?

[LecrisUT]

Since it is in zproject now are you able to regenerate and send a new PR for this?

I'm afraid that's beyond my understanding of the project, could someone else take over that?

[sphaero]

It's quite simple. If you have zproject installed just run gsl project.xml in the repo root and commit the changes.

#2311

[sphaero]

closing this one