VS: Improve workaround for CUDA -Xcompiler placement bug

In commit v3.9.0-rc1~431^2~6 (VS: Place CUDA host compiler options in
proper project file fields, 2017-03-07) we worked around a bug in the
CUDA VS integration by dropping `AdditionalCompilerOptions`.  However,
this silently drops `-Xcompiler=` options given by the user that don't
map to one of CudaCompile's dedicated settings.  Improve the workaround
to instead put the remaining `AdditionalCompilerOptions` into the
`AdditionalOptions` field behind `-Xcompiler=` ourselves.