feat: export sys variables from aws-lc-rs crate

[camshaft]

Description of changes:

This change exports the underlying *-sys crate in the aws-lc-rs crate. This is needed for a couple of reasons:

• In s2n-tls, we currently depend on the aws-lc-sys = "0.12". In s2n-quic, we depend on aws-lc-rs = ">=1.5". When a new aws-lc-rs version is published, then we get conflicting resolutions and end up with 2 copies of aws-lc-sys. Symbol prefixing is currently not working well enough to prevent conflicts.
• If crates depend on aws-lc-sys directly, they'll have to duplicate the fips/non-fips feature switching logic that's already present in aws-lc-rs. This logic is a bit complicated so it'd be nice to have it implemented in a single location.

With this change, s2n-tls will instead depend on aws-lc-rs = "1". This will avoid issues of preventing it using the latest aws-lc-sys crates on newer releases. It'll also make it easier to pick up fips builds, since we rely on the logic in aws-lc-rs.

Call-outs:

I did some minor refactoring to the build scripts to try and make it a bit clearer.

Testing:

I've expanded the sys-testing crate to include the new functionality.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3e194ee) 95.83% compared to head (4cf7dd5) 95.83%.

Additional details and impacted files

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##             main     #335   +/-   ##
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  Coverage   95.83%   95.83%           
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  Files          60       60           
  Lines        7868     7868           
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  Hits         7540     7540           
  Misses        328      328           

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