sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

sys/*/conf/*, docs: fix links to handbook

While here, fix all links to older en_US.ISO8859-1 documentation
in the src/ tree.

PR: 255026
Reported by: Michael Büker <freebsd@michael-bueker.de>
Reviewed by: dbaio
Approved by: blackend (mentor), re (gjb)
MFC after: 10 days
Differential Revision: https://reviews.freebsd.org/D30265

Port the NetBSD KCSAN runtime to FreeBSD.

Update the NetBSD Kernel Concurrency Sanitizer (KCSAN) runtime to work in
the FreeBSD kernel. It is a useful tool for finding data races between
threads executing on different CPUs.

This can be enabled by enabling KCSAN in the kernel config, or by using the
GENERIC-KCSAN amd64 kernel. It works on amd64 and arm64, however the later
needs a compiler change to allow -fsanitize=thread that KCSAN uses.

Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D22315