Use #if instead of #ifdef

swayidle/meson.build

@@ -1,18 +1,26 @@
 threads = dependency('threads')
 
+swayidle_deps = [
+	client_protos,
+	pixman,
+	wayland_client,
+	wayland_server,
+	wlroots,
+]
+
+if systemd.found()
+	swayidle_deps += systemd
+endif
+if elogind.found()
+	swayidle_deps += elogind
+endif
+
 executable(
 	'swayidle', [
 		'main.c',
 	],
 	include_directories: [sway_inc],
-	dependencies: [
-		client_protos,
-		pixman,
-		wayland_client,
-		wayland_server,
-		wlroots,
-		swayidle_deps,
-	],
+	dependencies: swayidle_deps,
 	link_with: [lib_sway_common, lib_sway_client],
 	install_rpath : rpathdir,
 	install: true