MFC 359047,359054: Deprecate procfs-based process debugging.

359047:
Mark procfs-based process debugging as deprecated for FreeBSD 13.

Attempting to use ioctls on /proc/<pid>/mem to control a process will
trigger warnings on the console. The <sys/pioctl.h> include file will
also now emit a compile-time warning when used from userland.

359054:
Fix the workaround to ignore the #warning for GCC.

clang and gcc use different warning flags for #warning preprocessor
directives.

For both 12 and 11, adjust the GCC warning flags to only be added in
4.7 and later since 4.2.1 does not support -Wno-cpp. For 11, add the
needed warning suppression to procctl's build. procctl was removed in
12.0.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add META_MODE support.

Off by default, build behaves normally.
WITH_META_MODE we get auto objdir creation, the ability to
start build from anywhere in the tree.

Still need to add real targets under targets/ to build packages.

Differential Revision: D2796
Reviewed by: brooks imp

The last big commit: let usr.sbin/ use WARNS=6 by default.

Use __FBSDID over rcsid[]. Protect copyright[] where needed.

The .Nm utility

Perform a major cleanup of the usr.sbin Makefiles.
These are not perfectly in agreement with each other style-wise, but they
are orders of orders of magnitude more consistent style-wise than before.

mdoc(7) police: removed HISTORY info from the .Os call.

Set WARNS=2 on programs that compile cleanly with it; add $FreeBSD$
where necessary.

Submitted by: Mike Barcroft <mike@q9media.com>

- Backout botched attempt to introduce MANSECT feature.
- MAN[1-9] -> MAN.

Set the default manual section for usr.sbin/ to 8.

mdoc(7) police: use canonical form of .Dd macro.

Cleanup manpage a bit.

Fix a buffer overflow.

PR: 16415
Submitted by: Kevin Day <toasty@dragondata.com>
Approved by: jkh

Fix various man pages to stop abusing the .Bx macro to generate
the string "FreeBSD". Use the .Fx macro instead.

$Id$ -> $FreeBSD$

This really belongs to section 8.

Use err(3). Change Synopsis to SYNOPSIS (needed for macro expansion) and
add SEE ALSO.

Add a copyright and license statement, at the request of Jordan.

Change the ioctls for procfs around a bit; in particular, whever possible,
change from

ioctl(fd, PIOC<foo>, &i);

to

ioctl(fd, PIOC<foo>, i);

This is going from the _IOW to _IO ioctl macro. The kernel, procctl, and
truss must be in synch for it all to work (not doing so will get errors about
inappropriate ioctl's, fortunately). Hopefully I didn't forget anything :).

explicitly set MAN8 since only MAN1 is defaulted.

Add $Id$

delete -static, add $Id$

First checkin of the procctl program.