nixos: add preferLocalBuild=true; on derivations for config files

nixos/modules/tasks/filesystems/vboxsf.nix

@@ -6,7 +6,7 @@ let
 
   inInitrd = any (fs: fs == "vboxsf") config.boot.initrd.supportedFilesystems;
 
-  package = pkgs.runCommand "mount.vboxsf" {} ''
+  package = pkgs.runCommand "mount.vboxsf" { preferLocalBuild = true; } ''
     mkdir -p $out/bin
     cp ${pkgs.linuxPackages.virtualboxGuestAdditions}/bin/mount.vboxsf $out/bin
   '';

nixos/modules/tasks/kbd.nix

@@ -15,6 +15,7 @@ let
   optimizedKeymap = pkgs.runCommand "keymap" {
     nativeBuildInputs = [ pkgs.buildPackages.kbd ];
     LOADKEYS_KEYMAP_PATH = "${kbdEnv}/share/keymaps/**";
+    preferLocalBuild = true;
   } ''
     loadkeys -b ${optionalString isUnicode "-u"} "${config.i18n.consoleKeyMap}" > $out
   '';

nixos/modules/tasks/network-interfaces.nix

@@ -995,7 +995,7 @@ in
       '';
 
     environment.etc."hostid" = mkIf (cfg.hostId != null)
-      { source = pkgs.runCommand "gen-hostid" {} ''
+      { source = pkgs.runCommand "gen-hostid" { preferLocalBuild = true; } ''
           hi="${cfg.hostId}"
           ${if pkgs.stdenv.isBigEndian then ''
             echo -ne "\x''${hi:0:2}\x''${hi:2:2}\x''${hi:4:2}\x''${hi:6:2}" > $out