Fix Clean target to not just delete output and intermediate directories
Fix Clean target to not just delete output and intermediate directories

In general, Clean should only clean up pieces produced by the build.
This way, when dropping to shared directories, builds don't delete
artifacts produced by other builds.

AArnott/nuproj,kovalikp/nuproj,DavidAnson/nuproj,DavidAnson/nuproj,ericstj/nuproj,PedroLamas/nuproj,oliver-feng/nuproj,faustoscardovi/nuproj,zbrad/nuproj,nuproj/nuproj,NN---/nuproj