The public dep for mesa has moved on to beyond llvm-18, but the
version we're compiling against is not supported by this change.
We workaround by ensuring that the llvm dep is less than 18 but
consistent with the clang version.
We use Mesa's gallium swrast to render as the driver with
Filament's backend set to GL. We provide a few scripts to parse
the tests (as jsons) and run gltf_viewer to produce the rendering.
