Changes

|Feature implementation notes=Note: time estimates here are total guesswork, erring on the safe side. Items are in no particular order.

## What: Bailouts are the heart of the optimizing compiler. When speculation fails (triggering a type, shape, overflow guard, etc), or C++ throws an exception, or needs to GC, we must be able to inspect the JIT frame, and if needed, reconstruct an interpreter frame.

## Dependencies:

### Frame reconstruction

## Priority: Critical, blocks testing

# '''Calls out to C++'''

## What: Ability to call into C++ from JIT code.