Add L4re support for arm

[sevenautumns]

This PR adds L4re support for arm with uclibc similar to previous PRs for L4re on x86.

I already tested these changes with a bootstrapped rust compiler using the L4Re Linker L4Bender as I described it in:
humenda/rustl4re#3

There is currently no arm L4re target in the official Rust repo.
And I do not know if it is a good Idea to add one right know since the linker L4Bender is not present:
rust-lang/rust#54425

[rust-highfive]

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.

[JohnTitor]

I assume you have a custom target for L4re, isn't it sufficient to have a fork libc as well?

[bors]

☔ The latest upstream changes (presumably #2403) made this pull request unmergeable. Please resolve the merge conflicts.

[JohnTitor]

Closing in favor of the above comment, feel free to re-open if there's a reason to have it on this crate.