The `fanotify` API[0] is a linux-specific API for notification and interception
of filesystem events. In some ways it is similar to `inotify`, but with
different advantages/tradeoffs. It is particularly well suited to full
filesystem/mount monitoring (vs per directory) and for allowing/denying access
to files (`inotify` lacks this capability).

The `fanotify` API has been updated several times since it was enabled in Linux
2.6.37. Presently I've only included support for the original `fanotify`
features, and the `FAN_MARK_FILESYSTEM` addition made in Linux 4.20. There are
subsequent updates in 5.0 and 5.1 not covered in this initial commit.

This commit adds the relevant constants and types from
`uapi/linux/fanotify.h`[1] and two new functions (`fanotify_init`[2] and
`fanotify_wrap`[3]) to `src/unix/linux_like/linux/mod.rs`. While I believe this
API is also present on Android I have presently limited my attention to Linux.

Although this commit focuses on Linux 4.20.x's `fanotify` API/constants I have
skipped adding constants for `FAN_ALL_CLASS_BITS`, `FAN_ALL_INIT_FLAGS`,
`FAN_ALL_MARK_FLAGS`, `FAN_ALL_EVENTS`, `FAN_ALL_PERM_EVENTS` and
`FAN_ALL_OUTGOING_EVENTS` even though they are present in this kernel version's
headers. These defines were deprecated[4] in later releases with instructions to
not use them in new programs or extend them with new values. It would be a shame
for new Rust programs to use deprecated #defines!

[0]: http://man7.org/linux/man-pages/man7/fanotify.7.html
[1]: https://github.com/torvalds/linux/blob/d54f4fba889b205e9cd8239182ca5d27d0ac3bc2/include/uapi/linux/fanotify.h
[2]: http://man7.org/linux/man-pages/man2/fanotify_init.2.html
[3]: http://man7.org/linux/man-pages/man2/fanotify_mark.2.html
[4]: https://github.com/torvalds/linux/commit/23c9deeb3285d34fd243abb3d6b9f07db60c3cf4#diff-4c9ca62be6bf38cc08f7ea9daf16e379

Clean up unnecessary link_name attributes

Haiku: add futimens and utimensat, remove futimes and cleanup.

Add triagebot configuration

This enables assignment through triagebot on this repository, in preparation for
the migration from highfive to triagebot for PR assignment.

 * Function futimes is not available in Haiku.
 * Functions futimens and utimensat are.
 * Cleanup some leftover cfg_attr attributes.

Add Lockf POSIX to UNIX targets

Add accept4() for NetBSD, Illumos and Solaris

Add copy_file_range to linux_like

Fix #1631

This is a Linux-only feature that was already present as a
syscall. Add it just to linux/gnu for the moment, as the musl version
bundled in the Rust's x86_64-unknown-linux-musl toolchain doesn't
include it yet.

Signed-off-by: Sergio Lopez <slp@redhat.com>

ci: allow overriding run-docker.sh CARGO_HOME.

The `ci/run-docker.sh` utility script adds a `--volume` argument to the
`docker` command to mount the Cargo home directory of the host machine
into the container at `/cargo`.

Prior to this patch the host's Cargo home directory is assumed to be the
`dirname` of the `dirname` of the `cargo` command's path. That works in
most cases where the host machine installed rust with vanilla
`rustup`. It may fail if the host machine used a different method.

For example if the host machine used the Archlinux rustup package[0]
then `cargo` is installed to `/usr/bin/cargo` and the `run-docker.sh`
script incorrectly mounts `/usr/` to the `/cargo` directory of the test
container.

This patch allows specifying an explicit `CARGO_HOME` to the
`ci/run-docker.sh` script so that users with a non-standard cargo dir
can use the utility without modification. By default if no `CARGO_HOME`
is set then the legacy behaviour is used and `CARGO_HOME` defaults to
the `dirname` of the `dirname` of the `cargo` command is used.

[0]: https://wiki.archlinux.org/index.php/rust#Arch_Linux_package

References:
* NetBSD (became available with 8.0):
  http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/socket.h?annotate=1.129&only_with_tag=MAIN
  http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/sys/accept4.c?annotate=1.2&only_with_tag=MAIN
* Illumos:
  https://illumos.org/man/3socket/accept
  https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/sys/socket.h
  https://github.com/illumos/illumos-gate/blob/master/usr/src/lib/libsocket/socket/weaks.c
* Solaris:
  https://docs.oracle.com/cd/E88353_01/html/E37843/accept-3c.html

Add definition of ucontext_t for macOS

Remove MSVC's wmemchr declaration

Bump version to 0.2.68

Add constants from `linux/in.h`

Add reenterant shadow.h functions

Enable `s390x-unknown-linux-gnu` on CI

Tweak `MAP_SYNC`

Add missing AT_ constants

Add AT_EACCESS to Linux, Solaris, and Fuchsia.

Add AT_SYMLINK_FOLLOW, AT_REMOVEDIR, and  _AT_TRIGGER to Solaris.

Unify mmap flags

add macOS mount flags

https://github.com/apple/darwin-xnu/blob/master/bsd/sys/mount.h#L288

Reduce checks for demoted apple 32-bit targets

Add F_OFD_* constants