The explicit selection of clang compiler should be only on UNIX.

When compiling on Windows with MSVC this option breaks the compilation.
Maybe this selection should be removed altogether and let the user
select its compiler when needed.

CMakeLists.txt

@@ -21,7 +21,6 @@ if(CUDA_FOUND)
   # to make sure more people can easily run class code without knowing 
   # about this compiler argument
   set(CUDA_NVCC_FLAGS "
-  -ccbin /usr/bin/clang; 
   -gencode;arch=compute_30,code=sm_30;  
   -gencode;arch=compute_35,code=sm_35;
   -gencode;arch=compute_35,code=compute_35;
@@ -32,6 +31,7 @@ if(CUDA_FOUND)
 
   # add -Wextra compiler flag for gcc compilations
   if (UNIX)
+    set(CUDA_NVCC_FLAGS ${CUDA_NVCC_FLAGS} "-ccbin /usr/bin/clang"
     set(CUDA_NVCC_FLAGS ${CUDA_NVCC_FLAGS} "-Xcompiler -Wextra")
     set(CMAKE_CXX_FLAGS "-stdlib=libstdc++")
   endif (UNIX)