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 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.

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

Declare `utmpx` on musl

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

VMADDR_CID_RESERVED is NOT available from Linux v5.6.
VMADDR_CID_LOCAL is available only on Linux >= v5.6.

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

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>

Add a declaration for `posix_fadvise64` on Linux.

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

Bump to 0.2.73

Remove unneeded release step

fix compilation errors

rustfmt

fix style

add f! for const fns

remove unneccessary const functions

rustfmt

Fix style errors

Also simplify some of the phrasing and perform minor grammar tweaks.

This incorporates the changes needed to cross-compile `rustc` for the
aarch64-apple-darwin target.

Revive CI for the switch target

Expose EPOLLEXCLUSIVE on illumos platform

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.

openbsd: Fix `WIFSTOPPED` following upstream

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

Limit macOS `$INODE64` symbol names to x86 and x86_64

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.