Expose si_pid and si_uid from siginfo_t as functions

Add CLD_ constants

The SIGCHLD variant of the siginfo structure also provides fields for
user and system time; expose those as well.

The first 3 fields of `siginfo_t` have different orders on MIPS. When
casting `siginfo_t` to a different type to access the fields of the
`sifields` union, avoid giving names to the first three fields, since
they're only present for memory layout and shouldn't be accessed from
the casted structure type.

 Add mac/ios pthread_from_mach_thread_np

On Linux, siginfo_t cannot expose these fields directly due to
https://github.com/rust-lang/libc/issues/716 , so expose them as
functions, just like si_addr and si_value.

In order to get alignment correct on both 32-bit and 64-bit
architectures, define an sifields union that includes a pointer field,
to ensure that it has the same alignment as a pointer.

These constants appear in the si_code field of a SIGCHLD signal or
waitid-returned siginfo value.

Allows us to get a pthread id from a match thread id.
From pthread.h [1]:

```
__API_AVAILABLE(macos(10.5), ios(2.0))
_Nullable pthread_t pthread_from_mach_thread_np(mach_port_t);
```

[1] - https://opensource.apple.com/source/libpthread/libpthread-416.40.3/pthread/pthread.h.auto.html

add openpty and forkpty implementation for illumos systems

At time of writing, illumos systems do not provide an implementation of
the openpty() and forkpty() wrappers provided on some other UNIX
systems.  While we expect to grow an implementation, it seems prudent to
provide a compatibility routine here first to unblock illumos support in
the popular nix crate.

DevkitPPC does not support unix sockets natively, meaning that bindings
to these functions was removed for powerpc targets with "nintendo" as
vendor.

Suggested target json files:

Nintendo Gamecube:
```
{
  "arch": "powerpc",
  "data-layout": "E-m:e-p:32:32-i64:64-n32",
  "dynamic-linking": false,
  "env": "newlib",
  "executables": true,
  "has-elf-tls": false,
  "has-rpath": true,
  "linker-flavor": "gcc",
  "llvm-target": "powerpc-eabi",
  "max-atomic-width": 32,
  "os": "dolphin",
  "target-c-int-width": "32",
  "target-endian": "big",
  "target-family": "unix",
  "target-mcount": "_mcount",
  "target-pointer-width": "32",
  "vendor": "nintendo"
}
```

Nintendo Wii:
```
{
  "arch": "powerpc",
  "data-layout": "E-m:e-p:32:32-i64:64-n32",
  "dynamic-linking": false,
  "env": "newlib",
  "executables": true,
  "has-elf-tls": false,
  "has-rpath": true,
  "linker-flavor": "gcc",
  "llvm-target": "powerpc-eabi",
  "max-atomic-width": 32,
  "os": "revolution",
  "target-c-int-width": "32",
  "target-endian": "big",
  "target-family": "unix",
  "target-mcount": "_mcount",
  "target-pointer-width": "32",
  "vendor": "nintendo"
}
```

Add more constants for getnameinfo on android

add ucred(3C) support for illumos and Solaris systems

This series of routines allows the caller to determine the credentials
of another process by pid, or of the process on the remote end of a UNIX
domain socket.  The ucred_t is an opaque object with accessor routines,
and must be freed through ucred_free(3C) after use.

Add sys/personality.h constants for Linux

Bump version to 0.2.74

Deprecate CTL_P1003_1B_MAXID

This change addresses two style errors found in PR review:
* indent and linebreak in CMSG_NXTHDR
* prefer `0 as *mut cmsghdr` over `core::ptr::nul_mut()`

This includes changes which will allow us to successfully build `libstd` for the PSP.

Create macros for defining Copy/Clone on enums and struct(), use for psp

It's been removed in FreeBSD 13 (svn r363622), and never had any
legitimate use outside of the base system anyway.

Fix styling

Re-run CI

This change defines and implements functions for the Fuchsia platform
corresponding to the C library CMSG_* macros, used for processing socket
control messages sent or received using the recv_msg(2)/send_msg(2)
syscalls.

Update FreeBSD 11 to 11.4-RELEASE

Add "_aligned_malloc" on windows platform

Use `build-std` feature instead of using `cargo-xbuild`

Add `PTRACE_EVENT_STOP`