|I want to port them to modern OS|
Very good learning experience, porting older code to modern practices.
|I want to create a cross-platform CMake project.|
A great XY problem.
Doing cross-platform is a good idea, restricting yourself to using CMake without knowing the complexity of CMake is the stumbling block.
|And for display I just need a bitblt support.|
More XY issues. Modern OS support for graphics is vastly different than DOS. Windows GDI comes closest, but that restricts you to one OS and a very outdated way to muck around with graphics.
You seem to be forgetting about multi-media support, sound and music. That is another layer of complexity added to what you need to learn.
What about keyboard/mouse/joystick support from your games? You do want the user to interact with the game, right?
| How to do that or which library to use for that purpose?|
That is the single question you should ask, no preconceptions of how to do something.
Three cross-platform libraries come to mind, supporting the full multi-media shebang. Graphics, music/sound, mouse/keyboard.
SFML (Simple and Fast Multimedia Library) - http://www.sfml-dev.org/index.php
SDL (Simple DirectMedia Layer) - http://www.libsdl.org/
SIGIL (Sound, Input, and Graphics Integration Library) - http://www.libsigil.com/