Warns about redundant 'static' keywords in unnamed namespace.

Change-Id: Iecab69161e24d73e39a8dd5baaba6929e12d4f29
Reviewed-on: https://gerrit.libreoffice.org/23679Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>