Adding ClangIR testing to debian-fast buildbot

[bcardosolopes]

If/when we get upstreamed, we should do this as early as possible. Creating an issue so I won't forget.

To do this:

1. Add a CMake flag that can control CIR being added.
2. Please add it to the existing builder to extra_configure_args here: https://github.com/llvm/llvm-zorg/blob/3bd1fe7602b89f268a0ef1bb5712ccd684b67f70/buildbot/osuosl/master/config/builders.py#L64