chromium: honor systemdSupport

This commit exposes that support for compilation without systemd,
controlled by the global systemdSupport argument.  This argument is
understood by many other nixpkgs expressions and can be set globally
in ~/.config/nixpkgs/config.nix.

pkgs/applications/networking/browsers/chromium/common.nix

@@ -23,7 +23,7 @@
 , libusb1, re2
 , ffmpeg, libxslt, libxml2
 , nasm
-, nspr, nss, systemd
+, nspr, nss
 , util-linux, alsa-lib
 , bison, gperf, libkrb5
 , glib, gtk3, dbus-glib
@@ -47,6 +47,8 @@
 , ungoogled ? false, ungoogled-chromium
 # Optional dependencies:
 , libgcrypt ? null # gnomeSupport || cupsSupport
+, systemdSupport ? stdenv.isLinux
+, systemd
 }:
 
 buildFun:
@@ -139,7 +141,7 @@ let
       libusb1 re2
       ffmpeg libxslt libxml2
       nasm
-      nspr nss systemd
+      nspr nss
       util-linux alsa-lib
       bison gperf libkrb5
       glib gtk3 dbus-glib
@@ -151,7 +153,8 @@ let
       libdrm wayland mesa.drivers libxkbcommon
       curl
       libepoxy
-    ] ++ optionals gnomeSupport [ gnome2.GConf libgcrypt ]
+    ] ++ optional systemdSupport systemd
+      ++ optionals gnomeSupport [ gnome2.GConf libgcrypt ]
       ++ optional gnomeKeyringSupport libgnome-keyring3
       ++ optionals cupsSupport [ libgcrypt cups ]
       ++ optional pulseSupport libpulseaudio;
@@ -204,9 +207,10 @@ let
       sed -i -e 's@"\(#!\)\?.*xdg-@"\1${xdg-utils}/bin/xdg-@' \
         chrome/browser/shell_integration_linux.cc
 
+    '' + lib.optionalString systemdSupport ''
       sed -i -e '/lib_loader.*Load/s!"\(libudev\.so\)!"${lib.getLib systemd}/lib/\1!' \
         device/udev_linux/udev?_loader.cc
-
+    '' + ''
       sed -i -e '/libpci_loader.*Load/s!"\(libpci\.so\)!"${pciutils}/lib/\1!' \
         gpu/config/gpu_info_collector_linux.cc