pkgs/mkSymlinks: add method to create arbitrary symlinks

pkgs/mk-symlinks.nix

@@ -0,0 +1,23 @@
+{ lib, stdenv }:
+
+{ name, symlinks }:
+let
+  normalized = lib.mapAttrs' (n: v: lib.nameValuePair (lib.path.subpath.normalise n) "${v}") symlinks;
+  linkCommands = lib.mapAttrsToList
+    (n: v: ''
+      mkdir -p $out/$(dirname ${n})
+      ln -s ${v} $out/${n}
+    '')
+    normalized;
+in
+stdenv.mkDerivation {
+  name = "firefox";
+  phases = [ "installPhase" ];
+  preferLocalBuild = true;
+  allowSubstitutes = false;
+  installPhase = ''
+    mkdir $out
+
+    ${lib.concatStringsSep "\n" linkCommands}
+  '';
+}