Dependency path wrapping + cleanup

[mazunki]

In order to more easily get clangd happy, I've set up ${dependency}.include and ${dependency}.lib targets to all deps/ (except lest, which is header-only. We should consider precompiling it), instead of requiring to guess these paths every time they're used.

I've also nixified deps/libfdt. Prior to this, we were hoping it was installed on the system, and somehow that was ok. Now we're properly depending on it.

Lastly, I've patched s2n-tls so that it actually compiles. It's still not linking due to -lgcc_eh, due to static builds... but better something than nothing.

[mazunki]

There is a question about include-paths of dependencies. Do we strictly want all dependencies to be placed in a subdirectory (unless, of course, this is already done upstream)? This seems to be a bit inconsistent.

Tests are good.

[mazunki]

The paths for lest don't seem to be fuully working just yet despite the include path being right. Probably missing something: ./test/lest_util/*.h should probably be part of ./deps/lest/utils or something instead. They're not a test.

[mazunki]

lest does work. It's just that some tests use top level declarations which confuses the LSP. Might wanna wrap them into a static specification[] array.

[mazunki]

Rebased to fix merge conflicts, but there's still the question of whether we want to strictly enforce including headers coming from dependency as #include <dependency/header.hpp>. I have separated include and include_root for this purpose.

[MagnusS]

I started reviewing this, but the changes are mixed with indentation updates (mainly due to added "let") and renamed files, making it hard to see your actual changes. Please move cleanup/formatting to a separate PR that only focusses on this

[MagnusS]

If no longer needed, just remove the line?

[mazunki]

There are some issues caused by reusing the same build/ directory between IncludeOS, tests and the example unikernel. I left the line around until this is properly fixed so it's easy to uncomment for now.