toybox: use structuredAttrs instead of passAsFile

pkgs/by-name/to/toybox/package.nix

@@ -43,7 +43,6 @@ stdenv.mkDerivation (finalAttrs: {
   postPatch = "patchShebangs .";
 
   inherit extraConfig;
-  passAsFile = [ "extraConfig" ];
 
   configurePhase = ''
     make ${
@@ -57,7 +56,8 @@ stdenv.mkDerivation (finalAttrs: {
         "defconfig"
     }
 
-    cat $extraConfigPath .config > .config-
+    printf "%s" "$extraConfig" > .config-
+    cat .config >> .config-
     mv .config- .config
 
     make oldconfig
@@ -87,6 +87,8 @@ stdenv.mkDerivation (finalAttrs: {
 
   env.NIX_CFLAGS_COMPILE = "-Wno-error";
 
+  __structuredAttrs = true;
+
   meta = {
     description = "Lightweight implementation of some Unix command line utilities";
     homepage = "https://landley.net/toybox/";