LLVM and Clang have nightly buildbots that check for regressions. They are quite fastidiously maintained. The project would really appreciate your help and you can do so by submitting a bug report with steps to reproduce and build artifacts. The bugfix will contain a test case, likely a minimal reduction of your repro, that will be run in the buildbots to make sure that you never see the same problem again.

And I do not believe that they have sacrificed anything to support both C and C++ (including partial support for their '11 variants). The codebase is abstracted away from the C/C++ differences where it makes sense. It is an impressively comprehensible compiler!

http://llvm.org/bugs/