A modified C compiler could be built that would do TCO. But, for this kind of application, it would mean that you'd have to re-validate your compiler, so that's pretty much not going to happen.
Looking it up, it seems that GCC (at least) presently does do (at some optimization levels) tail call elimination. Others probably do as well. I guess I've never looked it up because it was never relevant (if I'm using C, I might as well use for loops, they're at least as clear as the equivalent tail recursive function).
A modified C compiler could be built that would do TCO. But, for this kind of application, it would mean that you'd have to re-validate your compiler, so that's pretty much not going to happen.