Tree shaking keeps SPI/I2C even if not used

[mmoskal]

This program should have the same devs disasm regardless if the import is present or not

import { startBME680 } from "@devicescript/drivers"
console.log(Buffer.alloc)

[mmoskal]

branch: https://github.com/microsoft/devicescript/tree/var-when-used branch - but this requires some work with cell assignment in the compiler