The first three aren't a "trusting trust" attack. With the first three, any attack is visible in the code that you eventually compile. The whole point of "trusting trust" is no amount of source code inspection will ever uncover the problem.
Plus, Karger pointed out solution shortly after the problem: verified compiler, safe languages, repo security (esp paper in safes), crypto/courier distribution, and designed to build locally from source using onsite tools rerunning all tests, proofs, etc. Mitigates the need for worrying about Trusting Trust most of the time plus knocks out majority of attacks. Better to mention that if worried about subversion. Or Myer's landmark work that defined in detail problems and solutions.
Trusting Trust meme just misdirects focus from important issues.
But the person who did said
> you don't have to write a whole new compiler from scratch, unless you're worried about "trusting trust" attacks.
The point of that comment (at least, as I read it) isn't that you have to be worried about "trusting trust", but rather that there's no point in writing a new compiler from scratch unless you already are worried about "trusting trust" (with the implication being that most people aren't and so writing a new compiler from scratch isn't necessary).
SCM security issues (as you mentioned) are irrelevant at this point, because they really have no bearing on whether you have to write a new compiler from scratch.
[1]: https://www.ieee-security.org/TC/SP2016/papers/0824a018.pdf
Far as a compiler, that doesn't really matter for most systems (esp embedded). You can cross-compile to any architecture you want with portable code and a new backend. The only tools you need for each architecture's CPU's/MCU's are something to load and test the code. Those already exist in embedded sector. Instrumentation for Rust code would be necessary but this doesn't involve doing the whole compiler on, say, an 8-bitter.
"you don't have to write a whole new compiler from scratch, unless you're worried about "trusting trust" attacks."
That's an SCM security problem. You'd need to trust every compiler developer, the repo it's stored in, the transmission process, and whatever you used to build it. Most supposed solutions focus on the last one almost exclusively when the first three were the source of most attacks historically. In any case, that's barely relevant to the discussion of using Rust on a new architecture as almost nobody will every be hit by that & most people wanting Rust backends aren't doing high-assurance security for stopping nation-states or something. Those people hand-verify the assembly anyway.