malloc: Fix build with RECYCLE_BIG_ALLOCATIONS not defined

Libraries/LibC/malloc.cpp

@@ -174,12 +174,14 @@ static Allocator* allocator_for_size(size_t size, size_t& good_size)
     return nullptr;
 }
 
+#ifdef RECYCLE_BIG_ALLOCATIONS
 static BigAllocator* big_allocator_for_size(size_t size)
 {
     if (size == 65536)
         return &big_allocators()[0];
     return nullptr;
 }
+#endif
 
 extern "C" {