Replace libfdt's CMakeLists.txt with nix build

[mazunki]

I'm splitting up #2325 into standalone PRs for easier reviewing.

This was the only dependency which wasn't using default.nix in our list. It should be easier to manage our targets when everything follows the same structure.

[mazunki]

Tests are passing.

A quick search for libfdt suggests this is only relevant for aarch64, and there are no tests surrounding it.

[mazunki]

@elstr-512 , does this help you?

[elstr-512]

@elstr-512 , does this help you?

Probably! My current solution isn't great, I'm just inserting the libfdt/dtc dependency in overlay.nix.

...aarch64_inputs=ifself.stdenv.targetPlatform.system=="aarch64-linux"then[prev.pkgsStatic.dtc]else[];
...

[mazunki]

Let me know if this is missing something. I briefly saw you had a compiler too on your end which this doesn't provide. I suppose that's important?

[MagnusS]

From @elstr-512's branch it looks like we can use dtc from nixpkgs here so we don't have to maintain our own nix build for libfdt. I suggest we close this PR for now, then we can revisit when @elstr-512 submits the ARM build patches. It looks like ./deps/libfdt could then be removed completely.

[alfreb]

Yea, I agree, if we can use one from nixpkgs let's do that instead. But thanks @mazunki - getting a dependency with nix is better than getting it with cmake, so your solution would be an improvement as well.

[mazunki]

Understandable. I did see it existed upstream, but was concerned that if we needed to patch libfdt or upstream changed some behaviour in an update we would need to do this anyway. Either way, this is also good.