MFC 320675: Add deprecation notices for gdb and kgdb.

Even though gdb and kgdb may not be removed for 12.0 on some architectures,
the notice is unconditional as these tools will likely be removed at some
point in the future when adequate replacements are available (gdb in ports
or lldb in base).

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Add a new knob WITH_DEBUG_FILES to control the building of standalone
debug files for userland programs and libraries. The "-g" debug flag
is automatically applied when WITH_DEBUG_FILES is set.

The debug files are now named ${prog}.debug and ${shlib}.debug for
consistency with other systems and documentation. In addition they are
installed under /usr/lib/debug, to simplify the process of installing
them if needed after a crash. Users of bsd.{prog,lib}.mk outside of the
base system place the standalone debug files in a .debug subdirectory.
GDB automatically searches both of these directories for standalone
debug files.

Thanks to everyone who contributed changes, review, and testing during
development.

General mdoc(7) and typo fixes.

PR: 167696
Submitted by: Nobuyuki Koganemaru (kogane!jp.freebsd.org)
MFC after: 3 days

Remove mention of the -k and -wcore options because they don't
exist anymore.

PR: doc/70943
Submitted by: Jun <junsu at delphij dot net>
Reviewed by: delphij

Use the system gnuregex library vs. building GNU regex bits into libiberty
and using them.

Reviewed by: marcel,imp
Desired by: ache

Makefile (only) changes to allow building a cross debugger.

Fixed world breakage in the NOSHARED=yes case (missing library).

Fixed some style bugs.

Add bmake glue for gdb 6.1.1. Supports alpha, amd64, i386, ia64
and sparc64.

Note that the debugger doesn't support threading, nor kernel
debugging yet.