t/helper: mark unused argv/argc arguments

Many test helper programs do not bother to look at argc or argv, because
they don't take any options. In a user-facing program, it's a good idea
to check for unexpected arguments and complain. But for a test helper,
it's not worth the trouble to enforce this.

But we do want to tell the compiler we're OK with ignoring them, to
silence -Wunused-parameter (and obviously we can't get rid of them,
since we have to conform to the usual cmd__foo() interface).

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

t/helper/test-submodule-config.c

@@ -4,7 +4,7 @@
 #include "submodule-config.h"
 #include "submodule.h"
 
-static void die_usage(int argc, const char **argv, const char *msg)
+static void die_usage(int argc UNUSED, const char **argv, const char *msg)
 {
 	fprintf(stderr, "%s\n", msg);
 	fprintf(stderr, "Usage: %s [<commit> <submodulepath>] ...\n", argv[0]);