Add a simple unikernel which checks the fact that we can link with switch-installed libraries (and run it)

[dinosaure]

As asked here: #155 (comment)

[hannesm]

looks good to me. thanks.

[hannesm]

the only question I have is what the difference between "example" (directory in this repo) and "unikernel" is, and whether it is worth to describe (in README)? Is example still used?

[reynir]

I pushed a commit that adds a small README in the unikernel/ directory. When I come back to this repository in the future I would not be able to figure out why there is such a trivial example in unikernel/, and now it's documented in the README.

[hannesm]

And example is used as well in the CI actions...

[dinosaure]

I was not able to put the unikernel into the example directory due to dune which requires another manifest.c and another startup.c. I can try to merge the compilation of spt and xen into this example but I find the example/ quite complex in some way.

[reynir]

Would it be worthwhile to add a README in example/? Especially why we use fmt and not Printf.printf.

[dinosaure]

Replaced by 4fdf10e which is green and test what we want (without duplicate of unikernels and use the example/ directory).