linkage.c can be included by other programs as described in
docs/internal.txt (quote: "By using linkage.c instead of explicit
mail_link() calls, you are guaranteed that you will have a consistant
linkage among all software built on this system").

This commit adds linkage.c to staging.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Patch to compile with openssl 1.1

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>

most patches are added from Fedora

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>