[Santosh83]

Why stop with compilers? Inspect the circuit diagrams for all your hardware and then make sure the actual manufacturing followed the designs to a tee.

[Royalaid]

I mean I know it hyperbole but I am pretty sure there are hardware bugs that allow access, see that Intel or IBM remote management disclosure. It might not a real backdoor but it's as good as one. As people above are mentioning keep your paranoia inside your threat model