Basic frontend being prototyped in examples/sysir/frontend.janet. Still
a lot of work needs to be done here, and some of this code will
eventually move to C most likely, but this is a good way to better
exercise our backend.
Type inference - at the very least _forward_ inference, is the most
needed change here. While one could do this in the compiler
frontend, doing so in sysir/asm is not so much of an issue. "Inference"
here means inserting "bind" instructions when there is only a single
type that will work correctly.
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