backport: add stabilized HermitOS interface

[stlankes]

HermitOS is a unikernel and its interface to the kernel is provided by https://crates.io/crates/hermit-abi. In the meantime parts of the interface is stabilized and we want to integrated it into libc. Unstable version will be still provided by hermit-abi.

This PR is a backport of #3724 and doesn't have breaking changes. It just provides new functions to enter the kernel.

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[stlankes]

I forgot the error numbers and added to this PR.

[JohnTitor]

Do you think this breaks the existing usage? If so, I'd like to provide this only on 1.0 as it's a breaking change.

[stlankes]

No! I am pretty sure.

[Thomasdezeeuw]

Any update on this? We want to use it Mio as well.

[tgross35]

@stlankes I picked up the first commit as part of my backport bonanza, in https://github.com/rust-lang/libc/pull/3814. The second commit (5c7c7824, "add missing error numbers for HermitOS") seems like it is something that should go to main too. Could you create a new PR targeting main that makes that change? Comment @rustbot label +stable-nominated so it gets picked up in the next backport.

[tgross35]

This can probably just be closed once you create the new one, but

@rustbot author

[bors]

:umbrella: The latest upstream changes (presumably #3814) made this pull request unmergeable. Please resolve the merge conflicts.

[tgross35]

The backport of the first commit merged. I am going to go ahead and close this - but please feel free to put up a new PR with 5c7c7824253e6f3f4735cf253fe2c7e60ab94cd0, as mentioned above.

[Thomasdezeeuw]

Thanks @tgross35

[stlankes]

@stlankes I picked up the first commit as part of my backport bonanza, in #3814. The second commit (5c7c782, "add missing error numbers for HermitOS") seems like it is something that should go to main too. Could you create a new PR targeting main that makes that change? Comment @rustbot label +stable-nominated so it gets picked up in the next backport.

I will do it next week. After my vacation...