Add cmake flag to enable support for GnuPG's de-vs compliance

By default, libkleo shall ignore GnuPG's de-vs compliance. That's because
only certified distributions of Kleopatra, etc., must claim compliance.

(cherry picked from commit 1b1a86ffbd868645b3a8f207e3aba69fa03120f8)

• GnuPG-bug-id: T8245