Set UsedAttr instead of LangOpt.EmtiAllDecls (temporary implementation)
Split CodeGen and UsedAttr from commitTransaction into separate functionw.
codegen() really does emitAllDecls(); use new IncrementalParser interfaces.
Use new interface
Rebase to master/HEAD; split commitTransaction(); select needed parts in emitAllDecls().
Merge branch 'usedAttrInsteadOfEmitAllDecls'