libmedia: fixed minor leak in BDiscreteParameter::AddItem.

* CID 992460
rule FFilterByBuildFeatures: Fix output
DefineDefaultBuildProfiles: Various fixes

* Fix adding WebPositive optional package.
* Fix adding wonderbrush package. Add it only for gcc2 to avoid a
  warning by AddHaikuImagePackages.
* Simplify adding xz_utils package.