Complete quoting for parameters of some CMake commands

[elfring]

Some parameters (like "${SDL2_INCLUDE_DIR}") are passed to CMake commands in your build script 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.

[MrSapps]

Perhaps its worth changing the CI builds to have a space in the path on purpose to weed out these issues.