New module for bare metal architecture which still have a libc

[gbip]

This should fix #375 😄
Please tell me if there is anything wrong in this PR.

[rust-highfive]

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

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[gbip]

I think this is now ready for review 😄

[alexcrichton]

Thanks for the PR! This has come up a few times before:

• Add support for cfg(target_family = "none") #891
• Make libc build on unknown platforms. #753

Right now libc isn't targeted at providing a compatibility layer or polyfilling certain types and such on various platforms, but rather it's providing the bindings for a particular platform that match the C standard and/or popular C compilers. That means that we can't really add this target as it doesn't really match up to existing compilers as there's not really a concept of "no platform".

[gbip]

Could you please join the discussion in #375 ?

[gnzlbg]

@gbip Thank you for submitting this PR! I am going to close this PR since it appears that a change like this would require more consensus. Feel free to re-open if you disagree, or after more consensus is achieved.