KHR_pipeline_library is a base extension whose semantics can only
be exercised by extensions: EXT_graphics_pipeline_library
and KHR_ray_tracing_pipeline. Both remain gated under LLVM,
so advertising the KHR base extension is inert for conformant apps.
The reason for the change is a hard requirement for KHR_pipeline_library
in DXVK 2.7+. DX games under Proton, which uses DXVK, fail adapter
creation if this extension is absent. DXVK supports scenario when
KHR_pipeline_library is available but two dependent extensions aren't.
The !use_llvm condition originated in f1095260a4 when
KHR_pipeline_library was first wired up for ray tracing only. It was
touched also in 045c96d896 when EXT_graphics_pipeline_library also took
it as a dependency.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41134>
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