Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

elf-hints.h: Allow rtld_paths.h to be included before it

Currently rtld_paths.h will #undef _PATH_ELF_HINTS in order to override
this to the right value if included afterwards, but the other way round
does not work as elf-hints.h tries to define an already-defined macro to
a potentially different value. Thus, guard the definition here so that
rtld_paths.h's definition continues to take precedence.

Note that, although all in-tree uses of _PATH_ELF_HINTS have included
rtld_paths.h already, pax-utils wants _PATH_ELF_HINTS from elf-hints.h
and so we cannot just drop the define. In-tree uses must just continue
to make sure that they include rtld_paths.h to get the right value for
libcompat builds as is already required.

Reviewed by: kib, brooks, jhb, imp
Differential Revision: https://reviews.freebsd.org/D40918

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

include: General further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using mis-identified 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.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

* include/elf.h has been repo copied to include/elf-hints.h, and it no
longer includes machine/elf.h.
* consumers of elf.h now use the minimalist elf header possible.

This change is motivated by Binutils 2.11.0 and too much clashing over
our base elf headers and the Binutils elf headers.

$Id$ -> $FreeBSD$

Add hints file structures and defines.

Fill out the ELF header files to make them more or less complete.
Fix a macro name that was misspelled both in brandelf.c and
imgact_elf.h.