MFC after:	3 weeks

Obtained from:	NetBSD

Most notable, other than some style issues:
CVS 1.11:
  do not use LOG_CONS.
CVS 1.13:
  consistently use exit instead of return in main().
  use LOG_WARNING instead of LOG_ERR for non critical errors.

Obtained from:	NetBSD
MFC after:	2 weeks

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Sponsored by:	Dell EMC Isilon

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

Reduce overlinking