Fix modification of logging paths on Windows.
Fix modification of logging paths on Windows.

This change makes the previous commit work for Windows builds. Surprisingly,
CMake uses POSIX-style paths for Windows platforms as well, so the \ path separator
should not be used.

JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio