> clang, which is helped by the fact that there is a very clear, simple and DOCUMENTED boundary into LLVM
(1) People adding C++11 features to clang are not going to be dealing with LLVM, they're going to be modifying and extending clang's existing C++ parser. So however nice the clang-LLVM front-end-middle-end interface is, that's not going to have much impact on this job. Rather, what's important is the quality of clang's internal algorithms and data-structures (and those in gcc's c++ front-end). If clang does better there (dunno), that's great for them, but it has nothing to do with RMS's plugin position.
(2) RMS is not against clean code, nice interfaces, good data structures, and good documentation. His concerns (whether you agree with them or not) are the degree to which interfaces are expressed in a way that circumvents the GPL. Good interfaces don't circumvent the GPL;
So it's perfectly fine to clean up and document gcc's data structures and interfaces (and indeed, this is already happening, and has been for a long time). RMS isn't going to stop you.