CPU build.

Author: trivialfis

src/common/cuda_rt_utils.cc

@@ -3,6 +3,8 @@
  */
 #include "cuda_rt_utils.h"
 
+#include "cuda_stream.h"  // for StreamRef
+
 #if defined(XGBOOST_USE_CUDA)
 #include <cuda_runtime_api.h>
 

src/common/cuda_rt_utils.h

@@ -5,9 +5,7 @@
 #include <cstddef>  // for size_t
 #include <cstdint>  // for int32_t
 
-#if defined(XGBOOST_USE_CUDA)
-#include "cuda_stream.h"
-#endif
+#include "cuda_stream.h"  // for StreamRef
 
 namespace xgboost::curt {
 std::int32_t AllVisibleGPUs();

src/common/cuda_stream.h

@@ -2,14 +2,18 @@
  * Copyright 2022-2025, XGBoost contributors
  */
 #pragma once
+
+#if defined(XGBOOST_USE_CUDA)
 #include <cuda_runtime.h>
+#endif  // defined(XGBOOST_USE_CUDA)
 
 #include <memory>   // for unique_ptr
 #include <utility>  // for swap
 
 #include "common.h"
 
 namespace xgboost::curt {
+#if defined(XGBOOST_USE_CUDA)
 class StreamRef;
 
 class Event {
@@ -94,4 +98,7 @@ class Stream {
   void Sync() { this->View().Sync(); }
   void Wait(Event const &e) { this->View().Wait(e); }
 };
+#else
+class StreamRef {};
+#endif
 }  // namespace xgboost::curt