gnu: gnome-session: Add elogind input.

* gnu/packages/gnome.scm (gnome-session): Add elogind input, while
  disabling the use of systemd's journal.

gnu/packages/gnome.scm

@@ -3794,6 +3794,27 @@ such as gzip tarballs.")
               (sha256
                (base32
                 "0icajbzqf5llvp5s8nafwkhwz6a6jmwn4hhs81bk0bpzawyq4zdk"))))
+    (arguments
+     '(#:phases
+       (modify-phases %standard-phases
+         (add-before 'configure 'pre-configure
+           (lambda* (#:key outputs #:allow-other-keys)
+             ;; Use elogind instead of systemd.
+             (substitute* "configure"
+               (("libsystemd-login >= 183 libsystemd-daemon libsystemd-journal")
+                "libelogind")
+               (("systemd") "elogind"))
+             (substitute* "gnome-session/gsm-systemd.c"
+               (("#include <systemd/sd-login.h>")
+                "#include <elogind/sd-login.h>"))
+             ;; Remove uses of the systemd journal.
+             (substitute* "gnome-session/main.c"
+               (("#ifdef HAVE_SYSTEMD") "#if 0"))
+             (substitute* "gnome-session/gsm-manager.c"
+               (("#ifdef HAVE_SYSTEMD") "#if 0"))
+             #t)))
+       #:configure-flags
+       '("--enable-elogind")))
     (build-system glib-or-gtk-build-system)
     (native-inputs
      `(("glib:bin" ,glib "bin") ; for glib-compile-schemas, etc.
@@ -3801,7 +3822,8 @@ such as gzip tarballs.")
        ("intltool" ,intltool)
        ("xsltproc" ,libxslt)))
     (inputs
-     `(("gnome-desktop" ,gnome-desktop)
+     `(("elogind" ,elogind)
+       ("gnome-desktop" ,gnome-desktop)
        ("gsettings-desktop-schemas" ,gsettings-desktop-schemas)
        ("gtk+" ,gtk+)
        ("json-glib" ,json-glib)