Use [[maybe_unused]]

src/array-length.c

@@ -11,8 +11,8 @@
 #include <array.h>
 
 static void
-print_element (void *data,
-               void *user_data)
+print_element (                 void *data,
+               [[maybe_unused]] void *)
 {
     printf ("%" PRIdPTR " ", (intptr_t) data);
 }

src/hashtable-test.c

@@ -33,9 +33,9 @@ add_data (HashTable *table)
 }
 
 static void
-print_all (void *key,
-           void *value,
-           void *user_data)
+print_all (                 void *key,
+                            void *value,
+           [[maybe_unused]] void *)
 {
   printf ("%s:%s\n", (const char *) key, (const char *) value);
 }