patch 9.0.1390: FOR_ALL_ macros are defined in an unexpected file

Problem:    FOR_ALL_ macros are defined in an unexpected file.
Solution:   Move FOR_ALL_ macros to macros.h.  Add FOR_ALL_HASHTAB_ITEMS.
            (Yegappan Lakshmanan, closes #12109)
diff --git a/src/sign.c b/src/sign.c
index 64b64c9..8aa043b 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -2058,7 +2058,7 @@
     // Complete with name of sign groups already defined
     current_idx = 0;
     todo = (int)sg_table.ht_used;
-    for (hi = sg_table.ht_array; todo > 0; ++hi)
+    FOR_ALL_HASHTAB_ITEMS(&sg_table, hi, todo)
     {
 	if (!HASHITEM_EMPTY(hi))
 	{