Complete quoting for parameters of some CMake commands

[elfring]

Some parameters (like "${RAKNET_NAMED_INCLUDE_ONLY_DIR}" and "${RakNet_SOURCE_DIR}/Lib/DLL") are passed to CMake commands in your build scripts without enclosing them by quotation marks. I see that these places will result in build difficulties if the contents of the used variables will contain special characters like semicolons.

I would recommend to apply advices from a wiki article.