add initial support for csky-unknown-linux-gnuabiv2

[Dirreke]

Add libc-files to allow rust to be used on the csky/linux platform with a PR rust-lang/rust#113658 for rust

Signed-off-by: @Dirreke mingyang_ge@163.com

[rustbot]

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[Dirreke]

@rustbot review

[Dirreke]

I know the code to support Linux/csky isn't yet in rust itself; rust-lang/rust#113658 is in process. However, I need this crate merge first, and then rust-lang/rust#113658 ensues because rust depends on libc by using libc::c_char 、libc::c_int ...
Thanks!

[Dirreke]

@JohnTitor May I ask if you have time to review this PR? Thanks

[JohnTitor]

Could you rebase and squash commits into one?

[Dirreke]

Done! Thanks

[Dirreke]

@JohnTitor Could you merge it? Thanks!

[JohnTitor]

@bors r+

[bors]

📌 Commit 3d77fc6 has been approved by JohnTitor

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3d77fc6 with merge 92a5d3e...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-12, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14
Approved by: JohnTitor
Pushing 92a5d3e to main...