Work around CMake restriction since 3.25 on setting properties of targets built outside of project

[eyalroz]

When using cuda-api-wrappers through FetchContent, with recent CMake versions (3.25.3 and later, perhaps any 3.25), we get a complaint about this line:

target_link_libraries(CUDA::nvptxcompiler_static INTERFACE Threads::Threads) 

apparently, CMake doesn't like us doing that:

CMake Error at build/_deps/foo-src/CMakeLists.txt:80 (target_link_libraries):
  Cannot specify link libraries for target "CUDA::nvptxcompiler_static" which
  is not built by this project.

I think it's fine, and so did CMake up to v3.24, but - let's be courteous and make it a dependency of the wrappers, not the PTX compiler.