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)
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 a temporarily compatibility shim as well for kernels predating
close_range, since closefrom is used in some critical areas.
Reviewed by: markj (previous version), kib
Differential Revision: https://reviews.freebsd.org/D24399