Merge #43817: procps(-ng): enable systemd support

The whole closure only grows by 5 MiB roughly,
and it's all very common libraries (very low practical impact).

pkgs/os-specific/linux/procps-ng/default.nix

@@ -1,10 +1,16 @@
 { lib, stdenv, fetchurl, ncurses, pkgconfig
 
+# `ps` with systemd support is able to properly report different
+# attributes like unit name, so we want to have it on linux.
+, withSystemd ? stdenv.isLinux
+, systemd ? null
+
 # procps is mostly Linux-only. Most commands require a running Linux
 # system (or very similar like that found in Cygwin). The one
 # exception is ‘watch’ which is portable enough to run on pretty much
 # any UNIX-compatible system.
-, watchOnly ? !(stdenv.isLinux || stdenv.isCygwin) }:
+, watchOnly ? !(stdenv.isLinux || stdenv.isCygwin)
+}:
 
 stdenv.mkDerivation rec {
   name = "procps-${version}";
@@ -16,7 +22,8 @@ stdenv.mkDerivation rec {
     sha256 = "0r84kwa5fl0sjdashcn4vh7hgfm7ahdcysig3mcjvpmkzi7p9g8h";
   };
 
-  buildInputs = [ ncurses ];
+  buildInputs = [ ncurses ]
+    ++ lib.optional withSystemd systemd;
   nativeBuildInputs = [ pkgconfig ];
 
   makeFlags = [ "usrbin_execdir=$(out)/bin" ]
@@ -26,6 +33,7 @@ stdenv.mkDerivation rec {
 
   # Too red
   configureFlags = [ "--disable-modern-top" ]
+    ++ lib.optional withSystemd "--with-systemd"
     ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform)
     [ "ac_cv_func_malloc_0_nonnull=yes"
       "ac_cv_func_realloc_0_nonnull=yes" ];