Trent Mick points out that the BSD DB also provides an ndbm compatibility
layer.  If that is available, consider that as an option as well.
diff --git a/config.h.in b/config.h.in
index 8616811..9e4bdad 100644
--- a/config.h.in
+++ b/config.h.in
@@ -524,6 +524,9 @@
 /* Define if you have the <db_185.h> header file.  */
 #undef HAVE_DB_185_H
 
+/* Define if you have the <db1/ndbm.h> header file.  */
+#undef HAVE_DB1_NDBM_H
+
 /* Define if you have the <db.h> header file.  */
 #undef HAVE_DB_H