Including no keywords from extern "C" blocks

Change-Id: I8bcd7e8a492ee4dbfa5141416c7c038a1391cf20
Reviewed-on: https://gerrit.libreoffice.org/23673Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>