[Milpotel]

I'm not sure what C/C++ compilers you have in mind but bootstrapping older GCC and LLVM versions on modern systems is far from trivial and typically requires patching (e.g. older LLVM versions do not compile with modern compilers) and pinning a whole ecosystem (cmake, C lib, autotools, ...). The same is true for the other way around, modern C compilers usually do not compile on older systems and you get lucky if you find a round trip of several versions that get you a roughly working compiler at some point.