[R-package] correctly quote paths on Windows for CMake-based builds

[jameslamb]

Contributes to #5135.

I have a Windows laptop running Windows 10. It has an NVIDIA GeForce 840M GPU.

Software:

• R 4.2.1
• Rtools42
• CUDA Tookit 11.8 (link)

On latest master, running the following results in the unexpected symbol error reported in #5135.

Rscript build_r.R \
    --use-gpu \
    --boost-root="C:\Users\James\repos\LightGBM\external_libs\compute" \
    --no-build-vignettes \
    --use-msys2

With the changes on this branch, {lightgbm} compiles successfully.

Notes for Reviewers

This does not fix the other issue reported in #5135 (that CMake always finds the Boost bundled with RTools42). But it at least fixes how paths are handled and passed through build_r.R.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.