[gnome-flashback] build: add gdm dependency for screensaver

[Alberts Muktupāvels <muktupavels src gnome org>]

commit eb480aecafcf456f159c9ffbe6f0955f12184d00
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Feb 9 21:25:14 2020 +0200

    build: add gdm dependency for screensaver

 configure.ac | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/configure.ac b/configure.ac
index 77bf6b1..7bb5ad2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -221,6 +221,7 @@ PKG_CHECK_MODULES([SCREENCAST], [
 ])
 
 PKG_CHECK_MODULES([SCREENSAVER], [
+  gdm
   gio-unix-2.0 >= $GLIB_REQUIRED
   glib-2.0 >= $GLIB_REQUIRED
   gnome-desktop-3.0 >= $LIBGNOME_DESKTOP_REQUIRED