Libc update

[boustrophedon]

Summary of the PR

Updates libc and resolves #60.

There is no new or changed public functionality so I didn't update the changelog.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR have Signed-Off-By trailers (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[boustrophedon]

Whoops, minor fixup.

[boustrophedon]

\"\ cargo\ build\ --release\ --features=json
    Updating crates.io index
 Downloading crates ...
warning: spurious network error (2 tries remaining): failed to get successful HTTP response from `https://crates.io/api/v1/crates/proc-macro2/1.0.78/download`, got 503

Looks like crates.io had a blip and I'm not sure how to retry the build

[boustrophedon]

I moved the imports to the file they're actually used in mostly so that I could retry the build and it's passing now. I can move them back if anyone thinks they're better off in the bpf.rs file.