Mesa's Rusticl Driver Adds Optional OpenCL FP64 Support

The newest feature added by Red Hat engineer Karol Herbst to the Rusticl Mesa OpenCL open-source driver is FP64 support.

While not enabled by default even for GPUs with native FP64 capabilities, there is optional OpenCL double support now available with Mesa 23.2-devel.

As part of this new functionality, Rusticl picked up the infrastructure of using the new RUSTICL_FEATURES= environment variable for being able to specify features to dynamically enable at run-time. Thus with the latest five patches to Rusticl, setting RUSTICL_FEATURES=fp64 will enable this experimental OpenCL FP64 support.

More details on the Rusticl FP64 support in Mesa for those interested via this merge. Rusticl as this modern, Rust-written OpenCL Gallium3D driver continues evolving quite nicely and providing as a capable successor to the Clover Gallium3D driver within Mesa that is not actively maintained.