I think you could also make the case that the existing abstractions aren't actually fully deterministic themselves. The compiler or interpreter may not behave as it should. Therefore, for any correct C code, there's probability that the GCC compiler will turn it into correctly formed machine code. But it may not!
Is the probability much higher with GCC? Sure. But it's still a probability.
Is the probability much higher with GCC? Sure. But it's still a probability.