I think that one of the requirements that makes Go unsuitable as a C replacement in this specific case is the presence of the garbage collector. We need a language that we could use to write the garbage collector itself. It has to be a non-GC'd language or at least allow you to use it without linking to the GC.

I can see that being a problem if you were writing a garbage collector, but that's not a problem in this particular case (a C/C++ compiler).