Fix build on systems without systemd

backend/meson.build

@@ -25,7 +25,7 @@ backend_files = files(
 )
 
 if systemd.found()
-  wlr_files += files('session/logind.c')
+  backend_files += files('session/logind.c')
 endif
 
 lib_wlr_backend = static_library('wlr_backend', backend_files,

dummy.c

@@ -0,0 +1,2 @@
+// This is used to make meson happy
+void dummy(void);

meson.build

@@ -43,8 +43,6 @@ if systemd.found()
     add_project_arguments('-DHAS_SYSTEMD', language: 'c')
 endif
 
-wlr_files = []
-
 subdir('protocol')
 subdir('backend')
 subdir('render')
@@ -70,7 +68,7 @@ _wlr_deps = [
     math,
 ]
 
-lib_wlr = library('wlroots', wlr_files,
+lib_wlr = library('wlroots', files('dummy.c'),
     link_whole: [
         lib_wl_protos,
         lib_wlr_backend,