Update libc crate to 0.2.55

This change updates the libc crate to version 0.2.55.

Import subrepo libc/:libc at caf17a0641d29dc624621177f5756804dd180c13

1 files changed, 66 insertions, 0 deletions

diff --git a/libc/CONTRIBUTING.md b/libc/CONTRIBUTING.md
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+# Contributing to `libc`
+
+Welcome! If you are reading this document, it means you are interested in contributing
+to the `libc` crate.
+
+## Adding an API
+
+Want to use an API which currently isn't bound in `libc`? It's quite easy to add
+one!
+
+The internal structure of this crate is designed to minimize the number of
+`#[cfg]` attributes in order to easily be able to add new items which apply
+to all platforms in the future. As a result, the crate is organized
+hierarchically based on platform. Each module has a number of `#[cfg]`'d
+children, but only one is ever actually compiled. Each module then reexports all
+the contents of its children.
+
+This means that for each platform that libc supports, the path from a
+leaf module to the root will contain all bindings for the platform in question.
+Consequently, this indicates where an API should be added! Adding an API at a
+particular level in the hierarchy means that it is supported on all the child
+platforms of that level. For example, when adding a Unix API it should be added
+to `src/unix/mod.rs`, but when adding a Linux-only API it should be added to
+`src/unix/notbsd/linux/mod.rs`.
+
+If you're not 100% sure at what level of the hierarchy an API should be added
+at, fear not! This crate has CI support which tests any binding against all
+platforms supported, so you'll see failures if an API is added at the wrong
+level or has different signatures across platforms.
+
+With that in mind, the steps for adding a new API are:
+
+1. Determine where in the module hierarchy your API should be added.
+2. Add the API.
+3. Send a PR to this repo.
+4. Wait for CI to pass, fixing errors.
+5. Wait for a merge!
+
+### Test before you commit
+
+We have two automated tests running on [Travis](https://travis-ci.org/rust-lang/libc):
+
+1. [`libc-test`](https://github.com/alexcrichton/ctest)
+  - `cd libc-test && cargo test`
+  - Use the `skip_*()` functions in `build.rs` if you really need a workaround.
+2. Style checker
+  - `rustc ci/style.rs && ./style src`
+
+### Releasing your change to crates.io
+
+Now that you've done the amazing job of landing your new API or your new
+platform in this crate, the next step is to get that sweet, sweet usage from
+crates.io! The only next step is to bump the version of libc and then publish
+it. If you'd like to get a release out ASAP you can follow these steps:
+
+1. Update the version number in `Cargo.toml`, you'll just be bumping the patch
+   version number.
+2. Run `cargo update` to regenerate the lockfile to encode your version bump in
+   the lock file. You may pull in some other updated dependencies, that's ok.
+3. Send a PR to this repository. It should [look like this][example], but it'd
+   also be nice to fill out the description with a small rationale for the
+   release (any rationale is ok though!)
+4. Once merged the release will be tagged and published by one of the libc crate
+   maintainers.
+
+[example]: https://github.com/rust-lang/libc/pull/583