patch 9.0.0521: compiler warns for unused argument in small version

Problem:    Compiler warns for unused argument in small version.
Solution:   Add UNUSED.
diff --git a/src/drawline.c b/src/drawline.c
index d3eff84..07e2048 100644
--- a/src/drawline.c
+++ b/src/drawline.c
@@ -292,7 +292,7 @@
 	win_T		*wp,
 	winlinevars_T	*wlv,
 	int		sign_present UNUSED,
-	int		num_attr)
+	int		num_attr UNUSED)
 {
     if ((wp->w_p_nu || wp->w_p_rnu)
 	    && (wlv->row == wlv->startrow + wlv->filler_lines