Additionally, include cmath instead of math.h in dumperbase.hxx.

Change-Id: I0ee7158c86bdf266c783340bcf891aff44399066
Reviewed-on: https://gerrit.libreoffice.org/24632Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>