Are you saying that nvcc always does the C/C++ preprocessing rather than the host compiler, but since it knows the host compiler it attempts to emulate the host compiler’s conformance to the C/C++ preprocessor ?
That emulation seems like much work rather than let the host compiler handle the C/C++ preprocessor. On Windows Visual C++ is the host compiler and emulating the non-standard C/C++ preprocessor of Visual C++ is quite a task, and certainly has very little to do with the C/C++ preprocessor standard at any C++ level.
Does this emaulation of the host compiler’s C/C++ preprocessing change at all between a .cu file, with device and host code, and a normal C/C++ file ?