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

This adds various WASI libc definitions to the Rust libc bindings that I
needed while porting some applications to WASI.

It also removes the `pause` binding since newer versions of WASI libc
have removed this function as well. (WASI currently has no syscall with
this functionality.)

https://reviews.freebsd.org/rS357382

Plus, add new constants for sysctls that give names to existing magic numbers.

https://reviews.freebsd.org/rS350749
https://reviews.freebsd.org/rS352486

Wide chars are unsigned when normal chars are

sys/stat.h is a machine-independent header, but it has ifdefs for i386.
The version that was called x86_64.rs should be used on powerpc64 too,
but I don't have a machine to test that on.

I just got 'libxul.so: Undefined symbol "mq_close"' when rebuilding Firefox..
How did no one catch this before??

This is correct for both FreeBSD and DragonFly:
https://github.com/freebsd/freebsd/blob/master/lib/librt/Symbol.map
https://github.com/DragonFlyBSD/DragonFlyBSD/blob/e7ab884bd49753f8884eb597d10d6569a08fa0df/lib/librt/mq.c
https://github.com/DragonFlyBSD/DragonFlyBSD/blob/e7ab884bd49753f8884eb597d10d6569a08fa0df/lib/librt/aio.c

Hi,

Could you add some missing Haiku constants (i'm guessing they were added after Haiku port was last updated)?

These are defined in `unistd.h`: https://github.com/haiku/haiku/blob/194a45c6b4183083afdc7fac7b9e85f9162cdeb2/headers/posix/unistd.h#L134-L137

This ended up just getting copied from Linux as it appears to be the
same.

These declarations are the same as those for other platforms.

In particular:
Add timerfd constants and functions, from sys/timerfd.h.
Add EFD_SEMAPHORE and group all EFD_ constants together.
Add sigtimedwait function, from signal.h.
Add missing fallocate constants and functions, from linux/falloc.h and fcntl.h.
Add xattr functions, from sys/xattr.h.
Add SCHED_ and SEEK_ constants, from linux/sched.h and bits/seek_constants.h.
Add rlimit functions, from sys/resource.h.
Add RENAME_ constants, from stdio.h.
Add ino64_t type, from sys/types.h.

This commit defines ETIMEDOUT, SIGSTKSZ, MINSIGSTKSZ

SmartOS is a downstream distribution of illumos, and carries a number of
additional patches that are not commonly available in other illumos
distributions.  They are also not found in Oracle Solaris.  With these
removed, the libc tests pass on a stock illumos system running
OpenIndiana.

This is required on rust-lang/rust.