Remove $FreeBSD$: one-line sh pattern

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

Update libssp paths in various Makefile.depend* files

I've been advised that the model that uses these are fairly resilient, but
we do know the proper path to use (or remove, in the case of ^/targets/...),
so go ahead and update them to reflect that.

Add Makefile.depend.options

Leaf directories that have dependencies impacted
by options need a Makefile.depend.options file
to avoid churn in Makefile.depend

DIRDEPS for cases such as OPENSSL, TCP_WRAPPERS etc
can be set in local.dirdeps-options.mk
which can add to those set in Makefile.depend.options

See share/mk/dirdeps-options.mk

Reviewed by: bdrewery
MFC after: 1 week
Sponsored by: Juniper Networks
Differential Revision: https://reviews.freebsd.org/D22469