Remove $FreeBSD$: one-line sh pattern

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

Adopt SRCTOP in usr.bin

Prefer ${SRCTOP}/foo over ${.CURDIR}/../../foo and ${SRCTOP}/usr.bin/foo
over ${.CURDIR}/../foo for paths in Makefiles.

Differential Revision: https://reviews.freebsd.org/D9932
Sponsored by: Netflix
Silence on: arch@ (twice)

Convert to usr.bin/ to LIBADD
Reduce overlinking