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.

RFC 2235 - Implement PartialEq,Eq,Hash,Debug for all types

First pass at implementing [RFC2235](https://github.com/rust-lang/rfcs/blob/master/text/2235-libc-struct-traits.md). I just started with `PartialEq`/`Eq` and tested locally on my x64 Linux system. Definitely going to run into other types for other platforms that need this treatment, but thought I'd start small.

Open question is whether this should also rely on the `align` feature, which should improve which types can be auto-derived versus manually implemented (as it removed a lot of odd-sized padding arrays). My first pass here doesn't do that, but I might test it out to see if it does simplify quite a few structs. I think it might also be nice to have as it makes it easier for contributors to add new structs.

Part of rust-lang/rust#57715

Added inotify bindings.

Hi, I'd like to add inotify bindings. This is a first throw at it. Can you guide me through the process of merging it ?

Add powerpc64-unknown-freebsd

FreeBSD review: https://reviews.freebsd.org/D18367

This is used for running style checks on the libc codebase but shouldn't
be committed, so adding it to the .gitignore file.

This was not compile-tested on all platforms, but instead all `pub enum`
types had a `Debug` impl derived for them.

Add FreeBSD armv6 and armv7 targets

This was an artifact from when a git dependency on ctest was used. This
is no longer the case, so removing it to simplify future PRs.

Bump to 0.2.48

Bumps libc version to 0.2.48. This release contains the breaking changes performed in #1222 .

fix stack_t on FreeBSD

FreeBSD 10.x is EOL, in FreeBSD 11 and later, ss_sp is actually a void* [1]
dragonflybsd still uses c_char [2]

[1] https://svnweb.freebsd.org/base/releng/11.2/sys/sys/signal.h?revision=334459&view=markup#l438
[2] https://github.com/DragonFlyBSD/DragonFlyBSD/blob/master/sys/sys/signal.h#L339

should be committed with https://github.com/rust-lang/rust/pull/57810

dragonflybsd still uses c_char [2]

[1] https://svnweb.freebsd.org/base/releng/11.2/sys/sys/signal.h?revision=334459&view=markup#l438
[2] https://github.com/DragonFlyBSD/DragonFlyBSD/blob/master/sys/sys/signal.h#L339

Re-enable android build jobs

This performs a `yes | ./sdk/tools/bin/sdkmanager --licenses` - the sole purpose of the `--licenses` flag is to allow the user to accept all licenses a priori, so that all other commands don't show any licenses.

For some reason, after all licenses have been accepted, the install step says that some licenses are still not accepted... so we need to accept those too... Why? I have no idea, and accepting licenses while installing still appears to make things hang a little, but it only does so for one non-accepted license, instead of for 5-6 like before, so now things do work.

Closes #1170 .

Fix CMSG_DATA(3) and friends on BSD

PR #1098 added the CMSG_DATA(3) family of functions into libc.  Because
they're defined as macros in C, they had to be rewritten as Rust
functions for libc.  Also, they can't be tested in CI for the same
reason.  But that PR erroneously used the same definitions in BSD as in
Linux.

This commit corrects the definitions for OSX, FreeBSD, DragonflyBSD,
OpenBSD, and NetBSD.  I renamed a few variables and collapsed a few
macros in order to combine the definitions where possible.

Fixes #1210

PR #1098 added the CMSG_DATA(3) family of functions into libc.  Because
they're defined as macros in C, they had to be rewritten as Rust
functions for libc.  Also, they can't be tested in CI for the same
reason.  But that PR erroneously used the same definitions in BSD as in
Linux.

This commit corrects the definitions for OSX, FreeBSD, DragonflyBSD,
OpenBSD, and NetBSD.  I renamed a few variables and collapsed a few
macros in order to combine the definitions where possible.

Fixes #1210

Fix linking aio_read(3) and friends on NetBSD

The aio functions require librt on NetBSD.