Clone of https://github.com/NixOS/nixpkgs.git (to stress-test knotserver)

mesa: vdpau symlinks, broken after 1a52fdc

Fixes #17559. /cc @edolstra.
Using *relative* symlinks doesn't break when moving the files.

(cherry picked from commit 73e1242172d8012b1c6054a7f33bda1dc6f3bbc6)

+3 -3