MFC r358993: libssp: don't compile with -fstack-protector*

This similarly matches what we do in libc; compiling libssp with
-fstack-protector* is actively harmful. For instance, if the canary ctor
ends up with a stack protector then it will trivially trigger a false
positive as the canary's being initialized.

This was noted by the reporter as irc/ircd-hybrid started crashing at start
after our libssp was MFC'd to stable/11, as its build will explicitly link
in libssp. On FreeBSD, this isn't necessary as SSP bits are included in
libc, but it should absolutely not trigger runtime breakage -- it does mean
that the canary will get initialized twice, but as this is happening early
on in application startup it should just be redundant work.

MFC r356356, r356358, r356422: replace gcclibs' libssp

r356356:
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.

r356358:
libssp: fix FORTIFY_SOURCE stub declarations

The LSB 4.1 that I referenced omitted the varargs, and I failed to catch it.
The __vsnprintf_chk error was from just downright misreading the page. GCC6
caught all of these, but I had only tested GCC4.2.

r356422:
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.

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