Add CI check to be sure we do not regress on the hardening flags
Context
We have closed #317 (closed) now, this is about being sure we do not regress in the future (when we add a new library, for example)
Description
We can use https://github.com/slimm609/checksec.sh for this:
checksec --output csv -d /var/lib/flatpak/runtime/org.freedesktop.Sdk/x86_64/18.08/active/files/bin
Acceptance Criteria
CI jobs exist to check flags are correct