patch 8.1.1392: build failure in tiny version

Problem:    Build failure in tiny version.
Solution:   Define ex_popupclear to ex_ni if not implemented.  Add UNUSED.

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1392,
 /**/
     1391,
 /**/