Fix the VS generator to honor `COMPILE_OPTIONS` for CUDA. The exclusion
added by commit v3.9.0-rc1~431^2~7 (VS: Do not pass CUDA compile options
to C compiler, 2017-03-07) was correct but we need additional logic to
pass the CUDA compile options to the CUDA compiler. Also we should
still pass the CXX or C options to MSVC (ClCompile) when those languages
are enabled even if the link language is CUDA.
CUDA 8.0 MSBuild rules do not pass `-x cu` to nvcc and so cannot support
a custom file extension. Fix our test for this to use a `.cu` extension
instead.
Brad King