...so that the dynamic_cast is guaranteed to work on macOS (where RTTI
equivalence is determined by address, not by strcmp).  The relevant dynamic_castis in DocumentEventNotifier_Impl::processEvent in
dbaccess/source/core/dataaccess/documenteventnotifier.cxx, and at least during a
`make check` it appears to only be fed dbaccess::DocumentEventHolder (aka
comphelper::EventHolder<css::document::DocumentEvent>) instances also created in
documenteventnotifier.cxx (so the dynamic_cast happens to work fine also on
macOS in that case).  But better be conservative and mark EventHodler as
SAL_DLLPUBLIC_RTTI after all.

Change-Id: I99c842418d3f51265d96b8deb0dfc6c7a1540be5
Reviewed-on: https://gerrit.libreoffice.org/50258Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>