xous: add initial C definitions

[xobs]

This adds initial C definitions to Xous. There is no C library, so this mostly serves to add C-compatible exports to the libc crate.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @JohnTitor (or someone else) soon.

Please see the contribution instructions for more information.

[xobs]

Note that I have NOT added a file to libc/semver/ because Xous has no C functions, and so this file would be empty.

[JohnTitor]

We're pausing accepting external targets currently, see #3032 for details.

[xobs]

What is classified as an external target? Is it only tier 2 and lower?

[JohnTitor]

Ah I thought there was no official target for xous but it's not true (that's what we discussed in the above linked PR, read it for the context). r=me once the above is resolved.

[xobs]

Alright, I removed that commit. Note that the freebsd build is broken due to what apparently is a missing symbol in curl, preventing it from downloading things.

r=johntitor

[JohnTitor]

Thanks!

Note that the freebsd build is broken due to what apparently is a missing symbol in curl, preventing it from downloading things.

It has been fixed on master, it happens because the branch here is a bit old, so no problem at all :)

[JohnTitor]

Oh I forgot: @bors r+

[bors]

📌 Commit be1d79d has been approved by JohnTitor

It is now in the queue for this repository.

[bors]

⌛ Testing commit be1d79d with merge 7349741...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14
Approved by: JohnTitor
Pushing 7349741 to master...