patch 8.1.1633: cannot generate prototypes with X11 but without GUI

Problem:    Cannot generate prototypes with X11 but without GUI.
Solution:   Include X11/Intrinsic.h.
diff --git a/src/gui.h b/src/gui.h
index a16f098..dd1bbdc 100644
--- a/src/gui.h
+++ b/src/gui.h
@@ -29,6 +29,12 @@
 # include <gtk/gtk.h>
 #endif
 
+// Needed when generating prototypes, since FEAT_GUI is always defined then.
+#if defined(FEAT_XCLIPBOARD) && !defined(FEAT_GUI_MOTIF) \
+	&& !defined(FEAT_GUI_ATHENA) && !defined(FEAT_GUI_GTK)
+# include <X11/Intrinsic.h>
+#endif
+
 #ifdef FEAT_GUI_MAC
 # include <Types.h>
 /*# include <Memory.h>*/
diff --git a/src/version.c b/src/version.c
index 59c3c51..20bff05 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1633,
+/**/
     1632,
 /**/
     1631,