This does a few things: 1. Applications linked against a non-matching GBM can load the right version of the backend from the environment, avoiding GBM/Mesa version mismatches in many cases 2. Distros that want to split off libgbm into a separate package from the actual drivers get to not ship 40MB of libgallium_dri 3. The loader logic becomes way less complex See also: https://github.com/NixOS/nixpkgs/pull/338109 for original rationale. Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31074>