Following up on 7a4cc197 "Also on Linux do not
export symbols from static orcus libraries" that turned out to not be enough to
prevent ASan ODR violation reports after
f0aa1a78 "For Clang -fsanitize=vptr use
-fvisibility-ms-compat, not -fvisibility=hidden."  Given that liborcus is only
ever linked in as a static archive, it is hopefully OK (intended, even?) to not
export any of its symbols.

Change-Id: Ib8eb084def1725374747a389065bf8186218786e