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

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

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

Import the NetBSD Kernel Concurrency Sanitizer (KCSAN) runtime.

KCSAN is a tool to find concurrent memory access that may race each other.
After a determined number of memory accesses a cell is created, this
describes the current access. It will then delay for a short period
to allow other CPUs a chance to race. If another CPU performs a memory
access to an overlapping region during this delay the race is reported.

This is a straight import of the NetBSD code, it will be adapted to
FreeBSD in a future commit.

Sponsored by: DARPA, AFRL