Modify the nccl wrapper for --cupy-no-cuda

cupy/cuda/cupy_nccl.h

@@ -0,0 +1,45 @@
+// This file is a stub header file of cudnn for Read the Docs.
+
+#ifndef INCLUDE_GUARD_CUPY_NCCL_H
+#define INCLUDE_GUARD_CUPY_NCCL_H
+
+#ifndef CUPY_NO_CUDA
+
+#include <nccl.h>
+
+#else // #ifndef CUPY_NO_CUDA
+
+extern "C" {
+
+typedef struct ncclComm* ncclComm_t;
+
+enum {
+    NCCL_UNIQUE_ID_BYTES = 128
+};
+typedef struct {
+    char internal[NCCL_UNIQUE_ID_BYTES];
+} ncclUniqueId;
+
+typedef enum {
+    ncclSuccess
+} ncclResult_t;
+
+typedef enum {} ncclRedOp_t;
+
+typedef enum {} ncclDataType_t;
+
+const char* ncclGetErrorString(...);
+ncclResult_t ncclGetUniqueId(...);
+ncclResult_t ncclCommInitRank(...);
+void ncclCommDestroy(...);
+ncclResult_t ncclCommCuDevice(...);
+ncclResult_t ncclCommUserRank(...);
+ncclResult_t ncclAllReduce(...);
+ncclResult_t  ncclReduce(...);
+ncclResult_t  ncclBcast(...);
+
+}
+
+#endif // #ifndef CUPY_NO_CUDA
+
+#endif // #ifndef INCLUDE_GUARD_CUPY_NCCL_H

cupy/cuda/nccl.pyx

@@ -1,11 +1,13 @@
+# distutils: language = c++
+
 """
 Wrapper for NCCL: Optimized primiteive for collective multi-GPU communication
 """
 cimport cython
 
 from cupy.cuda cimport driver
 
-cdef extern from "nccl.h":
+cdef extern from "cupy_nccl.h":
     ctypedef struct ncclComm:
         pass
     ctypedef ncclComm* ncclComm_t