The all-zero Ed25519 public key is rejected by botan_pubkey_check_key()
when the key is loaded.
Note that Botan 3 requires GCC 11 or CLANG 14, i.e. can't easily be built
on Debian bullseye or Ubuntu 20.04.
The thread-local storage function gets flagged via various botan FFI
functions when using Botan 3, whitelist that instead of all of them.
If we check out and build a certain revision of a dependency in a branch and
switch to another that requires a different revision and then switch back,
the previous approach installed the wrong revision as it would incorrectly
assume the required revision was already built and ready to install.
ldconfig is required, otherwise the library won't be found by
strongSwan in the same session.
Should later be changed to 2.8.0 or a newer stable release.