foundationdb: add 5.2.5 release, and new 6.0.0 snapshot

This requires a bit of fiddling with the ldflags patches and reworking a few
things about how the SCM info is configured. Ideally, not much more will change
before the 6.0 release, I think...

This also upgrades all FoundationDB packages to use the ordinary libressl
expression (which is now at 2.7.x), and changes around a few other things,
which will require a rebuild.

Signed-off-by: Austin Seipp <aseipp@pobox.com>