tumbler: fix build deps QA warnings

WARNING: QA Issue: tumbler rdepends on libxml2, but it isn't a build dependency? [build-deps]
WARNING: QA Issue: tumbler rdepends on libgsf, but it isn't a build dependency? [build-deps]
WARNING: QA Issue: tumbler rdepends on libbz2, but it isn't a build dependency? [build-deps]

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>