Add elogind support

Resolves SirCmpwn/wlroots#146

backend/meson.build

@@ -28,9 +28,13 @@ if systemd.found()
 	backend_files += files('session/logind.c')
 endif
 
+if elogind.found()
+	backend_files += files('session/logind.c')
+endif
+
 lib_wlr_backend = static_library(
 	'wlr_backend',
 	backend_files,
 	include_directories: wlr_inc,
-	dependencies: [wayland_server, egl, gbm, libinput, systemd, wlr_protos],
+	dependencies: [wayland_server, egl, gbm, libinput, systemd, elogind, wlr_protos],
 )

backend/session/logind.c

@@ -5,8 +5,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
-#include <systemd/sd-bus.h>
-#include <systemd/sd-login.h>
 #include <unistd.h>
 #include <sys/sysmacros.h>
 #include <sys/stat.h>
@@ -15,6 +13,14 @@
 #include <wlr/backend/session/interface.h>
 #include <wlr/util/log.h>
 
+#ifdef HAS_SYSTEMD
+	#include <systemd/sd-bus.h>
+	#include <systemd/sd-login.h>
+#elif HAS_ELOGIND
+	#include <elogind/sd-bus.h>
+	#include <elogind/sd-login.h> 
+#endif
+
 enum { DRM_MAJOR = 226 };
 
 const struct session_impl session_logind;

backend/session/session.c

@@ -18,6 +18,8 @@ extern const struct session_impl session_direct;
 static const struct session_impl *impls[] = {
 #ifdef HAS_SYSTEMD
 	&session_logind,
+#elif HAS_ELOGIND
+	&session_logind,
 #endif
 	&session_direct,
 	NULL,