`setjmp`/`longjmp` support

We cannot support arbitrary `_setjmp`/`longjmp`, but if we see a `longjmp` we can probably avoid totally breaking the trace by resetting the stack, and ignoring future `ret`s underflowing our call stack (because we wouldn't know how many stack frames should have gotten popped).

They appear as `Call "_setjmp"` and `Call "longjmp"` tokens in the stream.

Start by locating where `Call "_setjmp"` and `Call "longjmp"` tokens are consumed in the trace stream. Follow the call-stack handling around these tokens and define the completed behavior as resetting the stack at `longjmp` and safely ignoring subsequent underflowing `ret` tokens without breaking the trace.

Written by the indexing model from the issue text.