You do not need a verifiable path to bootstrapping a toolchain to reduce surface area of attack to just the toolchain.

That being said, you could try building Clang with GCC and then GCC with Clang (or vice versa) to break any exploits designed to persist in either one indefinitely unless you are the victim of a really special hypothetical attack that targets both simultaneously, although I imagine you could interleave multiple GCC and Clang versions to make such an attack even harder to pull off or even add more compilers to the mix like EKOPath. That should reduce the attack surface area to binutils.