Complete quoting for parameters of some CMake commands

Some parameters (like “[`${CMAKE_CURRENT_SOURCE_DIR}/dfd2vk.inl`](https://github.com/KhronosGroup/dfdutils/blob/a80dd694522baf3afe52173addc3beebd80d1afb/CMakeLists.txt#L33-L52 "Update candidate")”) 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 the software documentation](https://cmake.org/cmake/help/v4.2/manual/cmake-language.7.html#lists "Description for CMake lists").

Start in CMakeLists.txt, especially the commands and parameters at lines 33-52, then read the linked CMake list documentation about quoting. Update the affected command arguments so variable values containing special characters remain safe, and verify that the project configures and builds successfully.

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