Fixes for nix-everything wrapper

1. Fix this eval error:
   https://hydra.nixos.org/jobset/nix/master#tabs-errors

   The dev package output (actually a separate derivation) needs to skip
   this for cross just as the main package output does.

2. Deduplicate libs attrset and list.

3. Move `nix-functional-tests` to `checkInputs`.

   With the Meson build system, we no longer need a `check` vs
   `install-check` distinction, so it is simpler to just keeep
   everything in one place.

src/perl/meson.build

@@ -82,6 +82,9 @@ nix_store_dep = dependency('nix-store')
 # pkgconfig available, are not in a standard location,
 # and are installed into a version folder. Use the
 # Perl binary to give hints about perl include dir.
+#
+# Note that until we have a better solution for this, cross-compiling
+# the perl bindings does not appear to be possible.
 #-------------------------------------------------
 perl_archname = run_command(
   perl, '-e', 'use Config; print $Config{archname};', check: true).stdout()