configure: rely on libplacebo to find vulkan

It detects it on Android and we don't. Since the vulkan code is only used with libplacebo, we should only enable it when libplacebo can use it (and the user allows it).

This should fail to build on Android before it's rebased on top of a60ff650.

changed milestone to %4.0

added Component::Build system label

added MRStatus::NotCompliant label

added 13 commits

• 79cd13f0...a60ff650 - 10 commits from branch videolan:master
• 1740258c - configure: use libplacebo pkg-config file to find optional components
• 42e89f29 - configure: disable libplacebo Vulkan code if the user doesn't want it
• e53d4d7b - configure: let libplacebo decide if it uses vulkan and with what version

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changed the description

That's not how we handle platform-specific library like OpenGL and we can provide vulkan without needing libplacebo.

I can keep the old detection in addition to the one already done by libplacebo, in case people don't use libplacebo. But in that case the code it will enable will also be compiled but never used. I don't see the point.

Point is, we don't need the one from libplacebo, we don't need to depend on an external dependency and buildsystem just to tell the buildsystem one package is not provided throught pkgconfig. Just write the proper detection for android (again, like we already do for Opengl here https://code.videolan.org/videolan/vlc/-/blob/master/configure.ac?ref_type=heads#L438-442, and here !6515 (d8c0fcd4))

I did that originally but then realized it's useless since there is no other use. The detection of the header is easy, but then if there are link flags needed that's just a wild guess per platform (ugly). Given the macOS build failure I assume it needs some C++ runtime in addition to some other libraries. That's all things we don't need to care about because libplacebo does all the dirty work for us. And then we don't need any of that without libplacebo.

Vulkan support doesn't depend on libplacebo support. The vulkan platform plugins can be used without libplacebo from out-of-tree modules or futures modules. It has been made specifically to avoid the strong dependency against libplacebo like we have for OpenGL. Don't break it.

(and again, don't depend on an external buildsystem when you can use standard buildsystem primitives with less work and more reliable behavior).

mentioned in merge request !7001 (merged)