disable security for bordervm "liminix" share

tftp needs to be able to follow symlinks into the store

bordervm-configuration.nix

@@ -108,6 +108,7 @@ in {
       };
       sharedDirectories = {
         liminix = {
+          securityModel = "none";
           source = builtins.toString ./.;
           target = "/home/liminix/liminix";
         };

overlay.nix

@@ -272,8 +272,15 @@ extraPkgs // {
     '';
   };
 
-  libusb1 = prev.libusb1.override {
+  libusb1 =
+    let u = prev.libusb1.overrideAttrs(o: {
+          # don't use gcc libatomic because it vastly increases the
+          # closure size
+          preConfigure = "sed -i.bak /__atomic_fetch_add_4/c\: configure.ac";
+        });
+    in u.override {
       enableUdev = final.stdenv.buildPlatform == final.stdenv.hostPlatform;
+      withDocs = false;
     };
 
   util-linux-small = prev.util-linux.override {