no_atomic: add mipsel-unknown-linux

[M1cha]

We're using yocto dunfell with the unofficial meta-rust layer and it doesn't add a libc suffix.

[taiki-e]

Thanks for the PR. As said in #751 (review), I would prefer not to accept a way to manually manage such a list of platforms.

That said, as said in #931 (comment), the current way is not ideal, and I would accept a PR that adopts the same way that the portable-atomic has adopted.

I believe the ideal solution here is to use cfg_target_has_atomic on Rust 1.60+ like my portable-atomic crate does.