add pktinfo consts and structs for linux and apple

The constants and structs are from `/usr/include/linux/in.h`, `/usr/include/linux/in6.h` for Linux (+ Android) and `/usr/include/netinet/in.h`, `/usr/include/netinet6/in6.h` for Apple.

With Apple it's important to mention that I'm choosing the RFC 3542 versions of the constants in alignment with other critical pieces of software like [nginx](http://hg.nginx.org/nginx/rev/9fb994513776), and Linux also defaults to this RFC version.

fix README.md links

Follow up to PR #977, which just fixed lib.rs while leaving similar broken links in README.md.

fix domain of html_root_url to be rust-lang.github.io

Fixes #976

haiku: Add RLIMIT_STACK and fix RTLD_* definitions

This commit adds additional definitions for Haiku which fixes issues in building libc and backtrace-rs when cross-compiling Haiku using docker ci.

Fix undefined-behavior on MacOSX structs in stdbuilds

Some MacOSX structs have an incorrect layout that results in undefined behavior. This is because on `x86_64` the MacOSX kernel headers define these using `#pragma pack 4`.

This PR fixes their layout using `repr(packed(4))` . Since it is only available on nightly, it is only enabled for stdbuilds .

feat: add fread_unulock for linux

add fread_unulock for linux

Make netlink struct fields public

I realized my netlink structs were a bit unusable if their fields are not public 🤦‍♂️

Follow up and improvement to #922

Refresh Cargo.lock

Fixes #968.

Fixes #968.

Add PTHREAD_*_MUTEX_INITIALIZER_NP for glibc

`pthread_mutex_t` varies across architectures, in several ways:
- endianness alters the ordering of bytes, since the contents of the
  struct are larger than 8-bit.
- its length varies.
- the location of the mutex kind (`PTHREAD_MUTEX_RECURSIVE`,
  `PTHREAD_MUTEX_ERRORCHECK` or `PTHREAD_MUTEX_ADAPTIVE_NP`) varies
  between 32-bit and 64-bit: On 32-bit architectures, it is preceded by
  three int/unsigned int, while on 64-bit architectures, it is preceded
  by four of them.

These initializers are only available from <pthread.h> when _GNU_SOURCE
is defined.

`pthread_mutex_t` varies across architectures, in several ways:
- endianness alters the ordering of bytes, since the contents of the
  struct are larger than 8-bit.
- its length varies.
- the location of the mutex kind (`PTHREAD_MUTEX_RECURSIVE`,
  `PTHREAD_MUTEX_ERRORCHECK` or `PTHREAD_MUTEX_ADAPTIVE_NP`) varies
  between 32-bit and 64-bit: On 32-bit architectures, it is preceded by
  three int/unsigned int, while on 64-bit architectures, it is preceded
  by four of them.

These initializers are only available from <pthread.h> when _GNU_SOURCE
is defined.

Relax the cfg_if check in ci/style.rs to allow #[cfg(target_endian)]
tests.

openbsd: SIGSTKSZ has been reduced

On OpenBSD 6.3, `SIGSTKSZ` value has changed.
https://github.com/openbsd/src/commit/e211c58cc8e20862a4eaa1b91fd4bc4a2975dad3

Add flock type value definitions for Linux/other/x86_64

Add MAP_STACK constant to OpenBSD

The mmap(2) flag indicate that the mapping is used as a stack.

https://man.openbsd.org/mmap.2#MAP_STACK
https://marc.info/?l=openbsd-tech&m=152035796722258&w=2

Default RHS to Self for Div and Shl

This fixes a consistency issue with the other operator traits.

This fixes a consistency issue with the other operator traits.

Add dox::{Copy, Clone} impls for pointer and integer types.

Fixes: #961

Fixes: #961

Fix libstd build for mips*-unknown-linux-uclibc

The getrandom syscall related constant were missing. This PR adds full syscall table just in case and few other nits.

netbsdlike: add TIOCSCTTY and TIOCSWINSZ ioctls.

Include ioctl commands for becoming controlling tty and setting window
size.  This enables https://github.com/jwilm/alacritty to be built and
run on OpenBSD 6.3.  NetBSD and kin share the same command constants.

Include ioctl commands for becoming controlling tty and setting window
size.  This enables https://github.com/jwilm/alacritty to be built and
run on OpenBSD 6.3.  NetBSD and kin share the same command constants.

Add MCL_CURRENT and MCL_FUTURE to s390.

Add strtonum to OpenBSD

OpenBSD provides [strtonum](http://man.openbsd.org/strtonum) but it is not in libc, yet.

Rename the dox configuration option to cross_platform_docs

The libc crate is used as a dependency of the Rust compiler. Its build system passes `--cfg dox` to all crates when generating their documentation. libc's documentation is generated when the build system is asked to generate the compiler documentation because `cargo doc` automatically documents all dependencies.

When the dox configuration option is enabled, libc disables its dependency on the core crate and provides the necessary definitions itself. The dox configuration option is meant for generating documentation for a multitude of targets even if the core crate for that target is not installed. However, when documenting the compiler, it's not necessary to do that; we can just use `core` or `std` as usual.

This change is motivated by the changes made to the compiler in rust-lang/rust#48171. With these changes, it's necessary to provide implementations of the `Clone` and `Copy` traits for some primitive types in the library that defines these traits (previously, these implementations were provided by the compiler). Normally, these traits (and thus the implementations) are provided by core, so any crate that uses `#![no_core]` must now provide its own copy of the implementations.

Because libc doesn't provide its own copy of the implementations yet, and because the compiler's build system passes `--cfg dox` to libc, generating the documentation for the compiler fails when generating documentation for libc. By renaming the configuration option, libc will use `core` or `std` and will thus have the necessary definitions for the documentation to be generated successfully.

**Note:** rust-lang/rust#48171 is blocked on this PR and on a release of libc including this change on crates.io. (Some crates in the compiler use libc as a submodule, while others use a version from crates.io.)