Zero-cost stack overflow checking

[dhalbert]

https://blog.japaric.io/stack-overflow-protection/

Describes how to put the stack at the bottom of RAM (with heap at the top) providing an automatic way to check overflow. Requires linking twice.

[dhalbert]

See micropython#4952 for Damien's ideas on this.

[tannewt]

This makes sense to me but we do actually allow for different stack bounds: https://github.com/adafruit/circuitpython/blob/master/shared-bindings/supervisor/__init__.c#L111

We could remove that if we like. I doubt we want to get in the business of moving the top of the stack on the fly.