PDB files not generated in debug mode

[andriyDev]

On Windows, CMake does not generate PDB files when compiling in debug mode. This can cause problems if the original CMake files try to use the PDB files.

For example, https://github.com/recastnavigation/recastnavigation lists the PDB file as an install file. This makes CMake panic.

The relevant flag that is needed to generate PDBs appears to be -Zi.