llama: consistent ctx <-> buf order for KV cache (#16746)

src/llama-model.cpp

@@ -2231,7 +2231,7 @@ bool llama_model::load_tensors(llama_model_loader & ml) {
     // define a comparator for the buft -> ctx map to ensure that the order is well-defined:
     struct ggml_backend_buft_comparator {
         bool operator()(const ggml_backend_buffer_type_t & lhs, const ggml_backend_buffer_type_t & rhs) const {
-            return ggml_backend_buft_name(lhs) < ggml_backend_buft_name(rhs);
+            return strcmp(ggml_backend_buft_name(lhs), ggml_backend_buft_name(rhs)) < 0;
         }
     };
     std::map<ggml_backend_buffer_type_t, ggml_context_ptr, ggml_backend_buft_comparator> ctx_map;