Ingo Weinhold 4bee3d6fb9 Add more rules to simplify dealing with build features
* Introduce the notion of build feature attributes and add rules
  SetBuildFeatureAttribute and BuildFeatureAttribute to set respectively
  get a build feature attribute.
* Add rule ExtractBuildFeatureArchives to download and extract archives
  and set build feature attributes to extracted entries.
* Add rule UseBuildFeatureHeaders as a shorthand for getting a build
  feature attribute and adding it as a system header search directory.
2013-05-06 04:31:27 +02:00
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