Hong Xu authored Aug 09, 2019 and Brad King committed Aug 20, 2019

Backslashes in `CUDA_NVCC_INCLUDE_DIRS` cause syntax errors because it
is written to a generated `.cmake` script as a string literal.  Use a
bracket argument to hold the expanded value as we already do for
`CUDA_NVCC_COMPILE_DEFINITIONS`.  Then explicitly convert backslashes to
forward slashes.