tools: avoid OpenSSL deprecation warnings

Our Gitlab CI buildsystem is set up to treat warnings as errors.
With OpenSSL 3.0 a lot of deprecation warnings occur.

With the patch compatibility with OpenSSL 1.1.1 is declared.
In the long run we should upgrade our code to use the current API.

A -Wdiscarded-qualifiers warning is muted by casting.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>