You're being pedantic, but your pedantry is incorrect, so allow me to be pedantic in correcting you :p. The output of all pure functions depends on the function and its inputs; this isn't more true for compilers than, say, addition. The problem with Trusting Trust is that the function isn't practically inspectable, not that the function is impure. A trusting trust compiler is still pure.

A functionally pure compiler would always provide the same output for the given source code. The challenges in creating repeatable builds of highly popular open source projects shows that the average compiler is anything but functionally pure. The global state of the system running the compiler has a huge impact on the output of the compiler.

I agree, but that's irrelevant to the Trusting Trust topic.

And even if you could manually verify the binary output of a compiler and prove it correct, you still don't know that the CPU itself is not malicious.