anchor.diff:  
       # set the default search path for DRI drivers; used e.g. by X server
       substituteInPlace "$dev/lib/pkgconfig/dri.pc" --replace '$(drivers)' "${driverLink}"
  -  '' + optionalString (!(stdenv.isArm || stdenv.isAarch64)) ''
  +  '' + optionalString (builtins.elem "intel" vulkanDrivers) ''
       # move share/vulkan/icd.d/
       mv $out/share/ $drivers/
       # Update search path used by Vulkan (it's pointing to $out but
  
positive.code:     "--with-dri-driverdir=$(drivers)/lib/dri"
      "--with-dri-searchpath=${driverLink}/lib/dri"
      "--with-egl-platforms=x11,wayland,drm"
    ] ++ (if stdenv.isArm || stdenv.isAarch64 then [
        "--with-gallium-drivers=nouveau,freedreno,vc4,etnaviv,swrast"
        "--with-dri-drivers=nouveau,swrast"
    ] else [
        "--with-gallium-drivers=svga,i915,ilo,r300,r600,radeonsi,nouveau,swrast"
        "--with-dri-drivers=i915,i965,nouveau,radeon,r200,swrast"
        ("--with-vulkan-drivers=intel" + optionalString enableRadv ",radeon")
    ]) ++ [
      (enableFeature enableTextureFloats "texture-float")
      (enableFeature grsecEnabled "glx-rts")
      (enableFeature stdenv.isLinux "dri3")
  
negative.code: { stdenv, fetchurl, fetchpatch, lib
  , pkgconfig, intltool, autoreconfHook, substituteAll
  , file, expat, libdrm, xorg, wayland, openssl
  , llvmPackages, libffi, libomxil-bellagio, libva
  