These constant can be used to determine the maximum number of iovecs can
be passed to functions like readv/writev.

Linux like uses UIO_MAXIOV, while the BSD family uses IOV_MAX.

Expose __errno_location() (introduced in DragonFlyBSD 5.8), which
returns the current thread's errno value. This is similar to Linux
and avoids having a separate module that defines both errno (which
depends on the thread_local feature) and an __error() function.

These methods were added in Haiku R1 beta 2.

Previously clock_getcpuclockid was enabled only on linux, with this
change it is enabled on all linux_like and freebsdlike.

Skip test on aarch64 due to https://github.com/rust-lang/libc/issues/1765

Linux defines a waitid type `P_PIDFD`, for use with process file
descriptors (`pidfd`). Add that constant.

In libc-test, add linux/wait.h to the Linux-specific and
Android-specific headers, to get the definition. Exclude it on Android
and musl for now, though, as the versions in CI don't have it yet.

On Linux, `sys/wait.h` defines a `W_STOPCODE` macro to construct a stop
code from the signal number of a stopping signal. Provide an equivalent
function.

Suggested-by: Ivan Tham <pickfire@riseup.net>

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.

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.

On Linux, `sys/wait.h` defines a `W_EXITCODE` macro to construct an exit
code from a return value and a signal number. Provide an equivalent
function.

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

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"
}
```

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.

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

Co-authored-by: Yuki Okushi <huyuumi.dev@gmail.com>

https://man7.org/linux/man-pages/man3/clock_getcpuclockid.3.html

In Linux we replaced VMADDR_CID_RESERVED with VMADDR_CID_LOCAL
in commit ef343b35d46667668a099655fca4a5b2e43a5dfe.
It is available since Linux v5.6, and it can be used to do
local communication if supported.

This patch deprecates VMADDR_CID_RESERVED for backward
compatibility.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

As with the other *64 functions in Linux, `posix_fadvise64` is like
`posix_fadvise` but uses `off64_t` instead of `off_t`.

Initially the EPOLLEXCLUSIVE definition was hidden on the illumos
platform as it lacked explicit support.  After further review, it was
concluded that EPOLLEXCLUSIVE can safely be considered a no-op, when not
fully implemented by the OS, making it safe for use on illumos.

https://github.com/openbsd/src/blob/b66614995ab119f75167daaa7755b34001836821/sys/sys/wait.h#L52

The new ARM-based platform doesn't need these as there's no legacy
constraints.

Tested via

**demo.c**

```c

int main() {
  fstat(0, NULL);
  fstatat(0, NULL, NULL, 0);
  lstat(NULL, NULL);
  stat(NULL, NULL);
  readdir(NULL);
  readdir_r(NULL, NULL, NULL);
}
```

**Compilation**

```none
% SDKROOT=/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk MACOSX_DEPLOYMENT_TARGET=11.5 cc -arch arm64 demo.c

% nm a.out
0000000100008030 d __dyld_private
0000000100000000 T __mh_execute_header
                 U _fstat
                 U _fstatat
                 U _lstat
0000000100003e64 T _main
                 U _readdir
                 U _readdir_r
                 U _stat
                 U dyld_stub_binder
```

This has also been experimentally compiled on a Developer Transition Kit.

Fixes #1775