patch 8.1.2163: cannot build with +spell but without +syntax

Problem:    Cannot build with +spell but without +syntax.
Solution:   Add #ifdef. (John Marriott)
diff --git a/src/drawline.c b/src/drawline.c
index 1415a31..9a4ff7d 100644
--- a/src/drawline.c
+++ b/src/drawline.c
@@ -1421,7 +1421,9 @@
 			syntax_attr = prev_syntax_attr;
 		    else
 		    {
+# ifdef FEAT_SPELL
 			can_spell = TRUE;
+# endif
 			syntax_attr = get_syntax_attr((colnr_T)v,
 # ifdef FEAT_SPELL
 						has_spell ? &can_spell :