Preventing atomic-context violations in Rust code with klint

The Rust standard library isn't available in Rust-for-Linux, only core (some of which is necessary to have Rust even work as a language e.g. you can't have for loops without core::iter::IntoIterator) is provided, plus their own take on alloc, but not std.

Even for writing very low level code, "This won't happen, don't bother me about it" is ergonomically necessary. It's fine if the reaction when you're wrong can be very dramatic, right down in the machine code if we have a fault but the CPU has for example not been told how to deal with any faults (or that the handlers for all faults are gone) it will just reboot.