patch 8.1.1307: cannot reconnect to the X server after it restarted

Problem:    Cannot reconnect to the X server after it restarted.
Solution:   Add the :xrestore command. (Adrian Kocis, closes #844)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index a2b302d..16f5059 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -394,6 +394,9 @@
 #ifndef FEAT_TERMINAL
 # define ex_terminal		ex_ni
 #endif
+#if !defined(FEAT_X11) || !defined(FEAT_XCLIPBOARD)
+# define ex_xrestore		ex_ni
+#endif
 
 /*
  * Declare cmdnames[].