Replace libstd with spin crate in cpu::cache_detected_features.

[briansmith]

Eliminate one of the two remaining problems with #![no_std] support
and reduce platform variance.

[elichai]

It seems that the failure of the test here is because of a network problem, I would just try to rerun it.
https://travis-ci.org/briansmith/ring/jobs/479666488

[elichai]

@briansmith If you could use version 0.4.10 instead it would be great, because 0.5.0 doesn't have feature(min_const_fn) and it's still an unstable feature in nightly-2018-10-01, so it doesn't compile at that version.
Then this would work with my PR to support sgx: #764

[elichai]

Suggested change

	spin = { version = "0.5.0", default-features = false }
	spin = "0.4.10"

This would support @baidu/rust-sgx-sdk and there are no features in spin so that disabling default-features isn't needed

[briansmith]

With this:

[target.'cfg(not(target_os = "ios"))'.dependencies]
spin = { version = "0.4.10", features = ["once"] }

I get:

error[E0554]: #![feature] may not be used on the stable release channel
#![cfg_attr(feature = "const_fn", feature(const_fn))]

So we have to use spin 0.5 in order for it to work on the stable channel.

IMO it would be much better to have the Baidu SGX SDK update the version of Rust it uses to a newer version. Is that not going to happen any time soon?

[elichai]

That's too bad.
I hope it will be soon
apache/teaclave-sgx-sdk#48

[elichai]

So this isn't relevant anymore, Sorry for the trouble.
I still don't think the default-features = false, I see no features in the toml: https://github.com/mvdnes/spin-rs/blob/master/Cargo.toml

[briansmith]

I still don't think the default-features = false, I see no features in the toml: https://github.com/mvdnes/spin-rs/blob/master/Cargo.toml

Thanks! I updated the PR to remove default-features = false.

[briansmith]

So, we can go ahead and do this, but if we do, this would be the first and only non-rust-lang crate that ring depends on. OTOH lazy_static does depend on spin itself it any crate has activated the spin_no_std feature, and we already depend on lazy_static (though we don't active spin_no_std ourselves).

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.

[coveralls]

Coverage increased (+0.01%) to 93.627% when pulling 4925653 on b/no_std_cpu-2 into c7f0ead on master.