CUDA target with -E hits assert

[rolandschulz]

clang++ -fsycl -fsycl-targets=nvptx64-nvidia-cuda -E empty.c
Results in the assert:

clang++: []/clang/lib/Driver/ToolChains/Cuda.cpp:677: virtual void clang::driver::toolchains::CudaToolChain::addClangTargetOptions(const llvm::opt::ArgList&, llvm::opt::ArgStringList&, clang::driver::Action::OffloadKind) const: Assertion `!GpuArch.empty() && "Must have an explicit GPU arch."' failed.