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libdevdctl: update deprecated deprecation warning comment

The comment indicated -Wno-deprecated-declarations was used to avoid
warnings about deprecated auto_ptr and various deprecated function
objects from <functional>. libdevdctl (now) does not use auto_ptr,
so don't mention it in the comment.

Sponsored by: The FreeBSD Foundation

Another round of attempting to squelch -Wdeprecated-declarations, which
has become very trigger-happy with libc++ 9.0.0.

It does not help that gcc's implementation of this warning is even more
trigger-happy, in the sense that it already warns on the declaration
itself, not when you are using it. This is very annoying with our use
of -Wsystem-headers. That should really be disabled for gcc.

Instead of disabling gcc's deprecated declaration warnings about e.g.
std::auto_ptr in a whole bunch of individual Makefiles, make the warning
globally non-fatal instead. This is similar to what was done to many
more non-fatal warnings from newer gcc versions.

Silence gcc warnings in libdevdctl about deprecated std::auto_ptr, and
various function objects from <functional>.

zfsd(8), the ZFS fault management daemon

Add zfsd, which deals with hard drive faults in ZFS pools. It manages
hotspares and replements in drive slots that publish physical paths.

cddl/usr.sbin/zfsd
Add zfsd(8) and its unit tests

cddl/usr.sbin/Makefile
Add zfsd to the build

lib/libdevdctl
A C++ library that helps devd clients process events

lib/Makefile
share/mk/bsd.libnames.mk
share/mk/src.libnames.mk
Add libdevdctl to the build. It's a private library, unusable by
out-of-tree software.

etc/defaults/rc.conf
By default, set zfsd_enable to NO

etc/mtree/BSD.include.dist
Add a directory for libdevdctl's include files

etc/mtree/BSD.tests.dist
Add a directory for zfsd's unit tests

etc/mtree/BSD.var.dist
Add /var/db/zfsd/cases, where zfsd stores case files while it's shut
down.

etc/rc.d/Makefile
etc/rc.d/zfsd
Add zfsd's rc script

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev.c
Fix the resource.fs.zfs.statechange message. It had a number of
problems:

It was only being emitted on a transition to the HEALTHY state.
That made it impossible for zfsd to take actions based on drives
getting sicker.

It compared the new state to vdev_prevstate, which is the state that
the vdev had the last time it was opened. That doesn't make sense,
because a vdev can change state multiple times without being
reopened.

vdev_set_state contains logic that will change the device's new
state based on various conditions. However, the statechange event
was being posted _before_ that logic took effect. Now it's being
posted after.

Submitted by: gibbs, asomers, mav, allanjude
Reviewed by: mav, delphij
Relnotes: yes
Sponsored by: Spectra Logic Corp, iX Systems
Differential Revision: https://reviews.freebsd.org/D6564