security/openvpn: run ldd -a when multi-link of "same" library found

The build runs a sanity to check that libssl and libcrypto are linked
only once, to catch mismatches in SSL providers to libpkcs11-helper
and openvpn itself. In order to assist the operator to find out
which libraries pull in differing versions of libcrypto or libssl,
run ldd -a in the error path. (Not run normally, not PORTREVISION bump.)

PR: 254323 (related)