CUDA: Work around VS limitation in CudaOnly.WithDefs test

CUDA 8.0 MSBuild rules do not pass `-x cu` to nvcc and so cannot support
a custom file extension.  Fix our test for this to use a `.cu` extension
instead.

Tests/CudaOnly/WithDefs/CMakeLists.txt

@@ -16,8 +16,15 @@ set(release_compile_defs DEFREL)
 #build a executable that needs to be passed a complex define through add_defintions
 #this verifies we can pass things such as '_','(' to nvcc
 add_definitions("-DPACKED_DEFINE=__attribute__((packed))")
-set_source_files_properties(main.notcu PROPERTIES LANGUAGE CUDA)
-add_executable(CudaOnlyWithDefs main.notcu)
+
+if(CMAKE_GENERATOR MATCHES "Visual Studio")
+  # CUDA MSBuild rules do not pass '-x cu' to nvcc
+  set(main main_for_vs.cu)
+else()
+  set(main main.notcu)
+  set_source_files_properties(main.notcu PROPERTIES LANGUAGE CUDA)
+endif()
+add_executable(CudaOnlyWithDefs ${main})
 
 target_compile_options(CudaOnlyWithDefs
   PRIVATE

Tests/CudaOnly/WithDefs/main_for_vs.cu

+#include "main.notcu"