Earlier quoted context omitted.
How would we know unless we can read (and compile) the source code?
Considering how few people read and compile the Linux source code, how do you know on Linux? Most distributions are binary, not source.
https://wiki.debian.org/ReproducibleBuilds
(I gave a talk about this at CCC. The status quo is a reason why free software doesn't have some of the transparency benefits over proprietary software we might expect, if you fear some developer is attacking you or someone is attacking some developers' infrastructure.)