trivial-builders.nix: Add input argument `passthru` to makeSetupHook

One significant use case is adding `passthru.tests` to setup-hooks,
and help increase test coverage for mission-critical setup-hooks.

As `meta`, `passthru` doesn't go into the build script directly.
However, passing an empty set to `passthru` breaks nixpkgs-review
and OfBorg tests, so pass it only when specified.

pkgs/build-support/setup-hooks/postgresql-test-hook/default.nix

···
 { callPackage, makeSetupHook }:
 
-(makeSetupHook {
+makeSetupHook {
   name = "postgresql-test-hook";
-} ./postgresql-test-hook.sh).overrideAttrs (o: {
   passthru.tests = {
     simple = callPackage ./test.nix { };
   };
-})
+} ./postgresql-test-hook.sh

pkgs/build-support/trivial-builders.nix

···
    *                 substitutions = { bash = "${pkgs.bash}/bin/bash"; };
    *                 meta.platforms = lib.platforms.linux;
    *               } ./myscript.sh;
+   *
+   * # setup hook with a package test
+   * myhellohookTested = makeSetupHook {
+   *                 deps = [ hello ];
+   *                 substitutions = { bash = "${pkgs.bash}/bin/bash"; };
+   *                 meta.platforms = lib.platforms.linux;
+   *                 passthru.tests.greeting = callPackage ./test { };
+   *               } ./myscript.sh;
    */
-  makeSetupHook = { name ? "hook", deps ? [], substitutions ? {}, meta ? {} }: script:
+  makeSetupHook = { name ? "hook", deps ? [], substitutions ? {}, meta ? {}, passthru ? null }: script:
     runCommand name
       (substitutions // {
         inherit meta;
         strictDeps = true;
+      } // lib.optionalAttrs (passthru != null) {
+        inherit passthru;
       })
       (''
         mkdir -p $out/nix-support