dnsmasq: honor dbusSupport

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

pkgs/tools/networking/dnsmasq/default.nix

@@ -1,13 +1,17 @@
-{ lib, stdenv, fetchurl, pkg-config, dbus, nettle, fetchpatch
-, libidn, libnetfilter_conntrack, buildPackages }:
+{ lib, stdenv, fetchurl, pkg-config, nettle, fetchpatch
+, libidn, libnetfilter_conntrack, buildPackages
+, dbusSupport ? stdenv.isLinux
+, dbus
+}:
 
 with lib;
 let
   copts = concatStringsSep " " ([
     "-DHAVE_IDN"
     "-DHAVE_DNSSEC"
-  ] ++ optionals stdenv.isLinux [
+  ] ++ optionals dbusSupport [
     "-DHAVE_DBUS"
+  ] ++ optionals stdenv.isLinux [
     "-DHAVE_CONNTRACK"
   ]);
 in
@@ -52,11 +56,12 @@ stdenv.mkDerivation rec {
     substituteInPlace $out/Library/LaunchDaemons/uk.org.thekelleys.dnsmasq.plist \
       --replace "/usr/local/sbin" "$out/bin"
   '' + optionalString stdenv.isLinux ''
-    install -Dm644 dbus/dnsmasq.conf $out/share/dbus-1/system.d/dnsmasq.conf
     install -Dm755 contrib/lease-tools/dhcp_lease_time $out/bin/dhcp_lease_time
     install -Dm755 contrib/lease-tools/dhcp_release $out/bin/dhcp_release
     install -Dm755 contrib/lease-tools/dhcp_release6 $out/bin/dhcp_release6
 
+  '' + optionalString dbusSupport ''
+    install -Dm644 dbus/dnsmasq.conf $out/share/dbus-1/system.d/dnsmasq.conf
     mkdir -p $out/share/dbus-1/system-services
     cat <<END > $out/share/dbus-1/system-services/uk.org.thekelleys.dnsmasq.service
     [D-BUS Service]
@@ -69,7 +74,8 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ pkg-config ];
   buildInputs = [ nettle libidn ]
-    ++ optionals stdenv.isLinux [ dbus libnetfilter_conntrack ];
+    ++ optionals dbusSupport [ dbus ]
+    ++ optionals stdenv.isLinux [ libnetfilter_conntrack ];
 
   meta = {
     description = "An integrated DNS, DHCP and TFTP server for small networks";