nsd: add switch to enable libsystemd (#422819)

pkgs/servers/dns/nsd/default.nix

@@ -4,6 +4,8 @@
   fetchurl,
   libevent,
   openssl,
+  pkg-config,
+  systemdMinimal,
   nixosTests,
   bind8Stats ? false,
   checking ? false,
@@ -16,6 +18,7 @@
   rootServer ? false,
   rrtypes ? false,
   zoneStats ? false,
+  withSystemd ? lib.meta.availableOn stdenv.hostPlatform systemdMinimal,
 
   configFile ? "/etc/nsd/nsd.conf",
 }:
@@ -33,10 +36,15 @@ stdenv.mkDerivation rec {
     substituteInPlace nsd-control-setup.sh.in --replace openssl ${openssl}/bin/openssl
   '';
 
-  buildInputs = [
-    libevent
-    openssl
-  ];
+  buildInputs =
+    [
+      libevent
+      openssl
+    ]
+    ++ lib.optionals withSystemd [
+      systemdMinimal
+      pkg-config
+    ];
 
   enableParallelBuilding = true;
 
@@ -55,6 +63,7 @@ stdenv.mkDerivation rec {
     ++ edf rootServer "root-server"
     ++ edf rrtypes "draft-rrtypes"
     ++ edf zoneStats "zone-stats"
+    ++ edf withSystemd "systemd"
     ++ [
       "--with-ssl=${openssl.dev}"
       "--with-libevent=${libevent.dev}"