As in, really disable, so that they do not even show. This moreover
avoids tons of D9025 warnings from MSVC about overriding -W4 with -w.

Change-Id: Ia2e72fd72d883d91bdd89e467ee42f259e2ae033
Reviewed-on: https://gerrit.libreoffice.org/72899
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>