Important things to add (Not necessarily in order)

Expand to way more builtins and assembly calls.
Deal with function calling, basic layouts, and all the fun basics of argument passing.
Add floats and some basic operations with them.
Add some more complex memory layouts and data types.
Add builtin function creation and calling. For many builtins, we should only need to create them if they are used as a function pointer. This may not be know at gen time for the specific function, so we might just have to add them all. Otherwise, many will always be inlined.
Add basic const folding? It should be really easy to add as an optimization. It should be a nice optimization for little cost. Just be sure to make it optional, otherwise our tests will do nothing.
Automatically build the zig builtins .o file and make it available here. We will need to link against it and use it whenever we call specific builtins.
Add unwind tables and landing pads.
Add ability to wrap functions with exceptions or return a results. Will need to start dealing with overflows and such to return errors.