any problems for source analysis tools: as one simple
        example, if you write "x-x" in your source code, the GCC AST will
        contain "0", with no mention of 'x'.  This is extremely bad for a
        refactoring tool that wants to rename 'x'.</li>
    <li>Clang can serialize its AST out to disk and read it back into another 
        program, which is useful for whole program analysis.  GCC does not have
        this.  GCC's PCH mechanism (which is just a dump of the compiler 
        memory