sys: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

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

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

arm64 lib32: prepare arm64 headers to redirect to arm

In order to compile lib32 libraries and other 32-bit code on arm64,
<machine/foo.h> needs to be redirected to an arm header rather
than arm64 when building with -m32. Ifdef the arm64 headers that
are installed in /usr/include/machine and used by user-level software
(including references from /usr/include/*.h) so that if __arm__ is
defined when including the arm64 version, <arm/foo.h> is included
rather than using the rest of the file's contents. Some arm headers
had no arm64 equivalent; headers were added just to do the redirection.
These files use #error if __arm__ is not defined to guard against
confusion. Also add an include/arm Makefile, and modify Makefiles
as needed to install everything, including the arm files in
/usr/include/arm. fenv.h comes from lib/msun/arm/fenv.h.

The new arm64 headers are:
acle-compat.h
cpuinfo.h
sysreg.h

Reviewed by: jrtc27, imp
Differential Revision: https://reviews.freebsd.org/D40944

Rationalize BSD license on sys/*/include/float.h

Remove the advertising clause from the Regents of the University of
California's license, per the letter dated July 22, 1999.

Update clause numbering.

Renumber clauses to avoid missing 3

Add the start of the arm64 machine headers. This is the subset needed to
start getting userland libraries building.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation