builtin: add a repository parameter for builtin functions

In order to reduce the usage of the global the_repository, add a
parameter to builtin functions that will get passed a repository
variable.

This commit uses UNUSED on most of the builtin functions, as subsequent
commits will modify the actual builtins to pass the repository parameter
down.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -331,7 +331,10 @@ cleanup:
 	return result;
 }
 
-int cmd_commit_graph(int argc, const char **argv, const char *prefix)
+int cmd_commit_graph(int argc,
+		     const char **argv,
+		     const char *prefix,
+		     struct repository *repo UNUSED)
 {
 	parse_opt_subcommand_fn *fn = NULL;
 	struct option builtin_commit_graph_options[] = {