Sayth Mark: [[ The initial issues that I observed when looking at JavaScriptCore was the Xcode project is generated in to a subdirectory. This prevents "xcodebuild installsrc" from working correctly (only the files in directories below the Xcode project appear to be installed). ]] This is easy to change once we're really to replace the existing project files, but I'm filing this bug do we don't forget.
More info from Mark on this topic: [[ Until this particular issue is addressed it's going to be very difficult for anyone at Apple to evaluate the correctness of the generated projects. ]]