Including no keywords from extern "C" blocks

Change-Id: Id0304994a692f1004993dda2ffd7fb819ab8e8d0
Reviewed-on: https://gerrit.libreoffice.org/23670Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>