Including no keywords from extern "C" blocks

Change-Id: I18ddafbf3d41f6779fb43e36ba1f1c48b37757a0
Reviewed-on: https://gerrit.libreoffice.org/23671Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>