GH-46147: [C++] Implement GCS support in Meson

[WillAyd]

Rationale for this change

This continues adding features to the Meson configuration (azure is already implemented)

What changes are included in this PR?

System-provided GCS can be leveraged to build optional GCS features. Note that this does not support Meson to automatically download GCS - GCS is a rather complicated CMake project and does not work well in the Meson/CMake subproject bridge. Another PR will have to implement that, due to its complexity (or ideally a Meson wrap for GCS is created)

Are these changes tested?

Yes

Are there any user-facing changes?

No

• GitHub Issue: [C++] Implement GCS Support in Meson #46147

[github-actions]

⚠️ GitHub issue #46147 has been automatically assigned in GitHub to PR creator.

[WillAyd]

This is some unfortunate indentation - opened an upstream issue at mesonbuild/meson#15032

[WillAyd]

This will be fixed in the next release of Meson

[WillAyd]

@kou could use some review on this if you get the chance. Thanks!

[raulcd]

Thanks for working on this @WillAyd ! LGTM.

Is the idea to have a follow up to provide some fallback similar to what we do if azure dependency is not found?

[WillAyd]

Yes eventually. I just didn't want that to be a blocker for now

[WillAyd]

For some more context @raulcd, for projects that don't have Meson configurations anywhere (whether in their source tree or in the wrapdb), Meson can even still auto-generate a configuration based off of CMake (as you see in our Azure wrap).

This works reasonably well for a few, smaller dependencies, but the more you add the more the auto-generated CMake wrapper struggles to resolve dependencies to other project dependencies. So I think its easier for larger projects like this just to assume a system installation first (that's all we test in CI now anyway) and leave it to a separate initiative to work out the kinks with the auto-generated config

[kou]

+1

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