config: mark unused callback parameters

The callback passed to git_config() must conform to a particular
interface. But most callbacks don't actually look at the extra "void
*data" parameter. Let's mark the unused parameters to make
-Wunused-parameter happy.

Note there's one unusual case here in get_remote_default() where we
actually ignore the "value" parameter. That's because it's only checking
whether the option is found at all, and not parsing its value.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -179,7 +179,7 @@ static int write_option_max_new_filters(const struct option *opt,
 }
 
 static int git_commit_graph_write_config(const char *var, const char *value,
-					 void *cb)
+					 void *UNUSED(cb))
 {
 	if (!strcmp(var, "commitgraph.maxnewfilters"))
 		write_opts.max_new_filters = git_config_int(var, value);