add, reset: use DIFF_OPT_SET macro to set a diff flag

Instead of explicitly setting the 'DIFF_OPT_OVERRIDE_SUBMODULE_CONFIG'
flag, use the 'DIFF_OPT_SET' macro.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/add.c

@@ -116,7 +116,7 @@ int add_files_to_cache(const char *prefix,
 	rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
 	rev.diffopt.format_callback = update_callback;
 	rev.diffopt.format_callback_data = &data;
-	rev.diffopt.flags |= DIFF_OPT_OVERRIDE_SUBMODULE_CONFIG;
+	DIFF_OPT_SET(&rev.diffopt, OVERRIDE_SUBMODULE_CONFIG);
 	rev.max_count = 0; /* do not compare unmerged paths with stage #2 */
 	run_diff_files(&rev, DIFF_RACY_IS_MODIFIED);
 	clear_pathspec(&rev.prune_data);

builtin/reset.c

@@ -166,7 +166,7 @@ static int read_from_tree(const struct pathspec *pathspec,
 	opt.output_format = DIFF_FORMAT_CALLBACK;
 	opt.format_callback = update_index_from_diff;
 	opt.format_callback_data = &intent_to_add;
-	opt.flags |= DIFF_OPT_OVERRIDE_SUBMODULE_CONFIG;
+	DIFF_OPT_SET(&opt, OVERRIDE_SUBMODULE_CONFIG);
 
 	if (do_diff_cache(tree_oid, &opt))
 		return 1;