You can bootstrap the compiler. It's a chore but not impossible. More usefully, you can check that your builds are identical to other people's, so at least your compiler isn't uniquely compromised.
https://www.schneier.com/blog/archives/2006/01/countering_tr...
https://www.gnu.org/software/mes/
The idea here, is that if you can get a very basic C compiler, you can start building TinyCC, and eventually build a pre-C++ version of GCC, and from there build up to modern GCC. This is a lot easier said than done of course, but not quite as bad as needing the original compilers from the 70s!
And specifically, only one person needs to do this once... I'm surprised there isn't some project doing this...