Well, if you are unsure if you can trust the second compiler (e.g. you didn't write it, audit it, bootstrap it yourself) you can just add a third (slightly more trustedworthy) compiler.
After that the infinite stack of turtles will take over and make sure it is asymptotically trustworthy.
After that the infinite stack of turtles will take over and make sure it is asymptotically trustworthy.