steamPackages.steam-fhsenv: fix Proton

LLVM must match version required by Mesa.

Fixes https://github.com/NixOS/nixpkgs/issues/127068

pkgs/development/libraries/mesa/default.nix

···
   passthru = {
     inherit libdrm;
     inherit (libglvnd) driverLink;
+    inherit llvmPackages;
 
     tests.devDoesNotDependOnLLVM = stdenv.mkDerivation {
       name = "mesa-dev-does-not-depend-on-llvm";

pkgs/games/steam/fhsenv.nix

···
 
     # dependencies for mesa drivers, needed inside pressure-vessel
     mesa.drivers
+    mesa.llvmPackages.llvm.lib
     vulkan-loader
     expat
     wayland
···
     xorg.libXdamage
     xorg.libxshmfence
     xorg.libXxf86vm
-    llvm_11.lib
     libelf
   ] ++ (if (!nativeOnly) then [
     (steamPackages.steam-runtime-wrapped.override {