Not true. See JavaScriptCore.xcodeproj in ...
http://www.opensource.apple.com/source/JavaScriptCore/JavaSc... http://svn.webkit.org/repository/webkit/trunk/Source/JavaScr...
... and if Xcode isn't your thing, just run the script "build-webkit" ...
http://svn.webkit.org/repository/webkit/trunk/Tools/Scripts/
... build instructions in plain English here ...