Allow installing rustfmt component to fail

Re-enable debug output in dox.sh and remove unused variable in runtest

Always use the latest ctest

Temporarily allow Android build jobs to fail

These are still too brittle for some reason.

Clean up documentation generation

Add IP[V6]_[RECV]ORIGDSTADDR for Linux and Android

Add support for illumos target

This change adds support for an illumos os target to libc.  Similar to the BSDs, there is a large deal of overlap (given the common history), so the 'solaris' directory was renamed to 'solarish' (it's the closest thing to an official term to refer to things descending from Solaris as well as Solaris).  There were also a number of missing definitions (as well as a couple missing functions) that have proved necessary for building a number of rust programs on illumos or Solaris.

Portions contributed by @papertigers .

Do not allow rustup to fail

Currently if rustup fails to download something the build will continue until that something is needed. This makes the job fail early and clearly.

and Solaris-derived distributions (i.e. illumos).  In addition, a number
of missing definitions (and compatability functions) that have been
found necessary to run a number of rust binaries on illumos have been
added.

Portions were contributed by Mike Zeller <mike@mikezeller.net>

unbreak openbsd after #1217

Fix license badge

Build all platforms

cc @alexcrichton this needs a more thorough review. It turns out libc failed to build on a lot of older Rust versions for various reasons and platforms, so it took a while to fix the build on all of them.

This PR fixes the build on all platforms and all Rust version down to the
minimum Rust version supported by libc: Rust 1.13.0.

The `build.rs` is extended with logic to detect the newer Rust features used by
`libc` since Rust 1.13.0:

* Rust 1.19.0: `untagged_unions`. APIs using untagged unions are gated on
  `cfg(libc_unions)` and not available on older Rust versions.

* Rust 1.25.0: `repr(align)`. Because `repr(align)` cannot be parsed by older
  Rust versions, all uses of `repr(align)` are split into `align.rs` and
  `no_align.rs` modules, which are gated on the `cfg(libc_align)` at the top
  level. These modules sometimes contain macros that are expanded at the top
  level to avoid privacy issues (`pub(crate)` is not available in older Rust
  versions). Closes #1242 .

* Rust : `const` `mem::size_of`. These uses are worked around with hardcoded
  constants on older Rust versions.

Also, `repr(packed)` structs cannot automatically `derive()` some traits like
`Debug`. These have been moved into `s_no_extra_traits!` and the lint of missing
`Debug` implementations on public items is silenced for these. We can manually
implement the `extra_traits` for these in a follow up PR. This is tracked
in #1243. Also, `extra_traits` does not enable `align` manually anymore.

Since `f64::to_bits` is not available in older Rust versions, its usage
has been replaced with a `transmute` to an `u64` which is what that method
does under the hood.

Closes #1232 .

This commit adds a `ci/build.sh` script that checks that libc builds correctly
for some common configurations (`--no-default-features`, `default`,
`extra_traits`) on most targets supported by Rust since Rust 1.13.0 (the oldest
Rust version that libc supports).

The build matrix is refactored into two stages.

The first stage is called `tools-and-build-and-tier1` and it aims to discover
issues quickly by running the documentation and linter builds, as well as
checking that the library builds correctly on all targets in all supported
channels and "problematic" Rust versions; Rust versions adding major new
features like `repr(align)`, `union`, etc. This first stage also runs
libc-test for the tier-1 targets on linux and osx. These builds finish
quickly because no emulation is necessary.

The second stage is called `tier2` and it runs libc-test for all other targets
for which we are currently able to do so.

Closes #1229 .

Check style using rustfmt and reformat

A couple of recent PRs attempt to reformat the library using rustfmt and run into issues against libc's style checker because rustfmt default settings differ.

This PR uses the rustfmt-preview from nightly to check that the library is appropriately formatted, adding a style as similar to libc's style as possible, so that both style checkers work properly simultaneously.

Fix cmsg(3) bugs for musl and OSX

This PR fixes bugs in the cmsg(3) family of functions for Linux/musl and OSX, introduced by PR #1098 and PR #1212 .  It also adds an integration test which hopefully will validate these functions on every platform.

Since these are defined in C as macros, they must be reimplemented in
libc as Rust functions.  They're hard to get exactly right, and they
vary from platform to platform.  The test builds custom C code that uses
the real macros, and compares its output to the Rust versions' output
for various inputs.

Skip the CMSG_NXTHDR test on sparc64 linux because it hits a Bus Error.

Issue #1239

Skip the entire cmsg test program on s390x because it dumps core
seemingly before the kernel finishes booting.

Issue #1240

This is an error from PR #1098.  The wrong definitions coincidentally
work on Linux/glibc, but fail on Linux/musl.

This was an oversight from PR #1212.  It's been revealed by the new cmsg
test.

Update runtest-android

Keep the implementation in sync with packed_simd and stdsimd.