Provide libssp based on libc

Provide libssp based on libc

For libssp.so, rebuild stack_protector.c with FORTIFY_SOURCE stubs that just
abort built into it.

For libssp_nonshared.a, steal stack_protector_compat.c from
^/lib/libc/secure and massage it to maintain that __stack_chk_fail_local
is a hidden symbol.

libssp is now built unconditionally regardless of {WITH,WITHOUT}_SSP in the
build environment, and the gcclibs version has been disconnected from the
build in favor of this one.

PR:		242950 (exp-run)
Reviewed by:	kib, emaste, pfg, Oliver Pinter (earlier version)
Also discussed with:	kan
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D22943