`/U`, `-U` 'undefine' argument not properly supported

[Colengms]

The 'undefine' (/U and -U) compiler args are not currently supported. Since is argument can be used to undefine even system defines, it would be necessary to keep track the 'undefines' (not just remove them from known defines), so the results of a compiler query can be post-processed to remove them from a configuration.