These sys/cdefs.h are not needed. Purge them. They are mostly left-over
from the $FreeBSD$ removal. A few in libc are still required for macros
that cdefs.h defines. Keep those.

Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D42385

(cherry picked from commit 559a218c9b257775fb249b67945fe4a05b7a6b9f)

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

-Werror warnings from clang 10.0.0, such as:

lib/libc/quad/fixdfdi.c:57:12: error: implicit conversion from 'long long' to 'double' changes value from 9223372036854775807 to 9223372036854775808 [-Werror,-Wimplicit-int-float-conversion]
                if (x >= QUAD_MAX)
                      ~~ ^~~~~~~~
/usr/obj/usr/src/powerpc.powerpc/tmp/usr/include/sys/limits.h:89:19: note: expanded from macro 'QUAD_MAX'
#define QUAD_MAX        (__QUAD_MAX)    /* max value for a quad_t */
                         ^~~~~~~~~~
/usr/obj/usr/src/powerpc.powerpc/tmp/usr/include/machine/_limits.h:91:20: note: expanded from macro '__QUAD_MAX'
#define __QUAD_MAX      __LLONG_MAX     /* max value for a quad_t */
                        ^~~~~~~~~~~
/usr/obj/usr/src/powerpc.powerpc/tmp/usr/include/machine/_limits.h:75:21: note: expanded from macro '__LLONG_MAX'
#define __LLONG_MAX     0x7fffffffffffffffLL    /* max value for a long long */
                        ^~~~~~~~~~~~~~~~~~~~

and many instances of:

lib/libc/quad/fixunsdfdi.c:73:17: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
        toppart = (x - ONE_HALF) / ONE;
                       ^~~~~~~~
lib/libc/quad/fixunsdfdi.c:45:19: note: expanded from macro 'ONE_HALF'
#define ONE_HALF        (ONE_FOURTH * 2.0)
                         ^~~~~~~~~~
lib/libc/quad/fixunsdfdi.c:44:23: note: expanded from macro 'ONE_FOURTH'
#define ONE_FOURTH      (1 << (LONG_BITS - 2))
                           ^  ~~~~~~~~~~~~~~~
lib/libc/quad/fixunsdfdi.c:73:29: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
        toppart = (x - ONE_HALF) / ONE;
                                   ^~~
lib/libc/quad/fixunsdfdi.c:46:15: note: expanded from macro 'ONE'
#define ONE             (ONE_FOURTH * 4.0)
                         ^~~~~~~~~~
lib/libc/quad/fixunsdfdi.c:44:23: note: expanded from macro 'ONE_FOURTH'
#define ONE_FOURTH      (1 << (LONG_BITS - 2))
                           ^  ~~~~~~~~~~~~~~~

Some of these routines exist in both lib/libc/quad/ and sys/libkern/.
r325988 ANSIfied sys/libkern.  Update libc/quad to match.

PR:		223641
Reported by:	bde
Sponsored by:	The FreeBSD Foundation

Mainly focus on files that use BSD 3-Clause license.

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.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by:	Jan Schaumann <jschauma@stevens.edu>
Pull Request:	https://github.com/freebsd/freebsd/pull/96

clause.

# If I've done so improperly on a file, please let me know.

I believe have made all of libc .c's as consistent as possible.