cmake fixes (#278)

csrc/scatter.h

@@ -2,7 +2,23 @@
 
 #include <torch/extension.h>
 
-int64_t cuda_version();
+#if (defined __cpp_inline_variables) || __cplusplus >= 201703L
+#define SCATTER_INLINE_VARIABLE inline
+#else
+#ifdef _MSC_VER
+#define SCATTER_INLINE_VARIABLE __declspec(selectany)
+#else
+#define SCATTER_INLINE_VARIABLE __attribute__((weak))
+#endif
+#endif
+
+namespace scatter {
+int64_t cuda_version() noexcept;
+
+namespace detail {
+SCATTER_INLINE_VARIABLE int64_t _cuda_version = cuda_version();
+} // namespace detail
+} // namespace scatter
 
 torch::Tensor scatter_sum(torch::Tensor src, torch::Tensor index, int64_t dim,
                           torch::optional<torch::Tensor> optional_out,

csrc/version.cpp

@@ -13,13 +13,15 @@ PyMODINIT_FUNC PyInit__version_cpu(void) { return NULL; }
 #endif
 #endif
 
-int64_t cuda_version() {
+namespace scatter {
+int64_t cuda_version() noexcept {
 #ifdef WITH_CUDA
   return CUDA_VERSION;
 #else
   return -1;
 #endif
 }
+} // namespace scatter
 
-static auto registry =
-    torch::RegisterOperators().op("torch_scatter::cuda_version", &cuda_version);
+static auto registry = torch::RegisterOperators().op(
+    "torch_scatter::cuda_version", &scatter::cuda_version);