Move to CMake and add options

[yegorich]

What about moving the build system to CMake and introduce compile-time options like, for example, ENABLE_BACKUP?

[pcercuei]

I like CMake so it would be a good option, but why would you need a switch for ENABLE_BACKUP? If you don't need it it's not in the way, so I think it's fine if it's built-in.

[yegorich]

The REAMDE.md states the following:

If you want to customize or remove the update mechanism, edit the perform_updates() function in mininit.c.

So if you don't need the backup mechanism that is on by default, you can disable it via specifying a CMake option like this:

cmake -DENABLE_BACKUP=OFF

This way, you don't need to modify the source code. The use case for this were, if you have constrained space and you cannot afford to maintain three images at once: rootfs, rootfs.bkp and update image.

[pcercuei]

What I mean, is that if you have the need for upgradable rootfs, just don't use it. It's not that much more code anyway.