postgresql: always create the $out/bin directory

This is needed because some PostgreSQL plugins don't have a bin
directory. If only these plugins are listed in cfg.extraPlugins buildEnv
will turn $out/bin into a symbolic link to ${pg}/bin. Lateron we try to
rm $out/bin/{pg_config,postgres,pg_ctl} which will then fail because
$out/bin will be read-only.

nixos/modules/services/databases/postgresql.nix

@@ -12,10 +12,13 @@ let
     else pkgs.buildEnv {
       name = "postgresql-and-plugins-${(builtins.parseDrvName pg.name).version}";
       paths = [ pg pg.lib ] ++ cfg.extraPlugins;
+      # We include /bin to ensure the $out/bin directory is created which is
+      # needed because we'll be removing files from that directory in postBuild
+      # below. See #22653
+      pathsToLink = [ "/" "/bin" ];
       buildInputs = [ pkgs.makeWrapper ];
       postBuild =
         ''
-          mkdir -p $out/bin
           rm $out/bin/{pg_config,postgres,pg_ctl}
           cp --target-directory=$out/bin ${pg}/bin/{postgres,pg_config,pg_ctl}
           wrapProgram $out/bin/postgres --set NIX_PGLIBDIR $out/lib