How to turn off CUDA completely with clang?

I have some *.cu files which are effectively empty on systems that don’t have CUDA.
But clang attempts to use CUDA whenever it meets the *.cu files and
I tried -nocudainc -nocudalib but now it complains about ptxas saying:

clang-12: error: unable to execute command: Executable “ptxas” doesn’t exist!
clang-12: error: ptxas command failed with exit code 1 (use -v to see invocation)

I just want clang to treat *.cu files as normal C++ files.
How can I achieve it?

Thanks.

Try clang++ -x c++ <file.cu>.