sys: Remove $FreeBSD$: two-line .h pattern

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

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

x86/include/elf.h: make inclusion blocks for elf32.h and elf64.h similar

They were copy-pasted when x86/include/elf.h file was merged from its
i386 and amd64 counterparts. Having the text around inclusions
significantly different is somewhat confusing.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D37085

i386: move hard-coded load address for PIE below default linker base

both for i386 native and compat32 amd64. We know the ld-elf.so.1 size
in advance, it fits there. Trying to push it up after the end of a
binary cannot work reliably and eventually fail for large binaries.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D37085

x86: clean up empty lines in .c and .h files

Consolidate identical ELF auxargs type defintions.

All platforms except powerpc use the same values and powerpc shares a
majority of them.

Go ahead and declare AT_NOTELF, AT_UID, and AT_EUID in favor of the
unused AT_DCACHEBSIZE, AT_ICACHEBSIZE, and AT_UCACHEBSIZE for powerpc.

Reviewed by: jhb, imp
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D17397

sys/x86: further adoption of SPDX licensing ID tags.

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.

Add AT_HWCAP2 ELF auxiliary vector.
- allocate value for new AT_HWCAP2 auxiliary vector on all platforms.
- expand 'struct sysentvec' by new 'u_long *sv_hwcap2', in exactly
same way as for AT_HWCAP.

MFC after: 1 month
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D12699

Add AT_EHDRFLAGS and AT_HWCAP on amd64.

x86 has two separate (but identical) list of AT_* constants and the
earlier commit to add AT_HWCAP only updated the i386 list.

Add AT_HWCAP and AT_EHDRFLAGS on all platforms.

A new 'u_long *sv_hwcap' field is added to 'struct sysentvec'. A
process ABI can set this field to point to a value holding a mask of
architecture-specific CPU feature flags. If an ABI does not wish to
supply AT_HWCAP to processes the field can be left as NULL.

The support code for AT_EHDRFLAGS was already present on all systems,
just the #define was not present. This is a step towards unifying the
AT_* constants across platforms.

Reviewed by: kib
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D12290

Convert machine/elf.h, machine/frame.h, machine/sigframe.h,
machine/signal.h and machine/ucontext.h into common x86 includes,
copying from amd64 and merging with i386.

Kernel-only compat definitions are kept in the i386/include/sigframe.h
and i386/include/signal.h, to reduce amd64 kernel namespace pollution.
The amd64 compat uses its own definitions so far.

The _MACHINE_ELF_WANT_32BIT definition is to allow the
sys/boot/userboot/userboot/elf32_freebsd.c to use i386 ELF definitions
on the amd64 compile host. The same hack could be usefully abused by
other code too.