Add support for LoongArch64

[heiher]

This PR is depends on the stable inline asm to unblock builds. All tests and benchmarks are passed. We will add CI support after LoongArch64 is promoted to Tier 2.

[workingjubilee]

If Amanieu was willing, a new feature for nightly-only asm! architectures could be added to this crate. It would look like adding this to the top of lib.rs:

#![cfg_attr(feature = "nightly-arch", feature(asm_experimental_arch))]

and this to Cargo.toml, under [features]:

# enable experimental nightly features
nightly-arch = []

And then gating mod loongarch behind #[cfg(feature = "nightly-arch")], with perhaps a bit more effort to make the tests work.

Of course, I am not Amanieu, so I do not know if he is willing. However, it seemed better to suggest it as an alternative to waiting for the stabilization timeframe to elapse, as that might prove longer than desired. My apologies if it is not a welcome suggestion.

[Amanieu]

Looks good overall!

For CI support, my recommendation would be to add a loongarch target to cross which works for Tier 3 targets.

Regarding inline asm, I think it's fine to wait for it to become stable since it's not too far off. If you need support sooner, I'm also happy to add it under an optional feature like @workingjubilee suggests.

[syrusakbary]

Hey @Amanieu, could it be possible to get this reviewed/merged soon? Thanks!

[Amanieu]

@heiher This PR is still marked as a draft, but I believe it is ready for review?

[heiher]

@heiher This PR is still marked as a draft, but I believe it is ready for review?

Nice!

[Amanieu]

Published.

[heiher]

Published.

Thank you.