x11/xorg: stdenv.lib -> lib in meta generator

The library does not depend on stdenv, that stdenv exposes lib is
an artifact of the ancient origins of nixpkgs.

I didn’t run the generator since it takes quite a while, but it should
be automatically done the next time somebody updates a package.

pkgs/servers/x11/xorg/generate-expr-from-tarballs.pl

@@ -311,7 +311,7 @@ foreach my $pkg (sort (keys %pkgURLs)) {
     hardeningDisable = [ "bindnow" "relro" ];
     nativeBuildInputs = [ pkgconfig $nativeBuildInputsStr];
     buildInputs = [ $buildInputsStr];$extraAttrsStr
-    meta.platforms = stdenv.lib.platforms.unix;
+    meta.platforms = lib.platforms.unix;
   }) {};
 
 EOF