hashmap: mark unused callback parameters

Hashmap comparison functions must conform to a particular callback
interface, but many don't use all of their parameters. Especially the
void cmp_data pointer, but some do not use keydata either (because they
can easily form a full struct to pass when doing lookups). Let's mark
these to make -Wunused-parameter happy.

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

strmap.c

@@ -2,10 +2,10 @@
 #include "strmap.h"
 #include "mem-pool.h"
 
-int cmp_strmap_entry(const void *hashmap_cmp_fn_data,
+int cmp_strmap_entry(const void *UNUSED(hashmap_cmp_fn_data),
 		     const struct hashmap_entry *entry1,
 		     const struct hashmap_entry *entry2,
-		     const void *keydata)
+		     const void *UNUSED(keydata))
 {
 	const struct strmap_entry *e1, *e2;