vte: respect the global systemdSupport flag

This commit allows to compile vte without systemd (-D_systemd=false)
if the systemdSupport attribute is set to false.  This can be done
globally in nixpkgs.conf, and is understood by other packages.  See
also PR #160972.

pkgs/development/libraries/vte/default.nix

@@ -21,6 +21,7 @@
 , zlib
 , icu
 , systemd
+, systemdSupport ? stdenv.hostPlatform.isLinux
 }:
 
 stdenv.mkDerivation rec {
@@ -63,6 +64,7 @@ stdenv.mkDerivation rec {
     pcre2
     zlib
     icu
+  ] ++ lib.optionals systemdSupport [
     systemd
   ];
 
@@ -73,6 +75,10 @@ stdenv.mkDerivation rec {
     pango
   ];
 
+  mesonFlags = lib.optionals (!systemdSupport) [
+    "-D_systemd=false"
+  ];
+
   postPatch = ''
     patchShebangs perf/*
     patchShebangs src/box_drawing_generate.sh