Yup, there are many, many times when I want to be able to do simple things with C or C++ code. Writing a little static analyzer tool that can check some internal code for a practice we have found harmful, parse some headers to automatically generate python bindings, documentation stubs, generate
really good unit tests stubs with the information the ast give you, grab all of the comments and run your own verification on them, automagically re-write code to not use an old api anymore. And this is all just with using the source parser side of things of llvm
These are the tools I write, they are not big commercial enterprises, most of them are one off projects that are used and tossed away within a year, very few are ever published. Clang makes me more productive because they give me the ability flat out do this type of thing. It doesn't matter what GNU political agenda is, their tool flat out doesn't let me do this like llvm can. As long as this is the case long term I will use llvm more and more over gcc.