make native and crust functions conform to x86-64 ABI

[crabtw]

• add functions to classify argument and return types
• convert argument and return types of native function in shim function
• convert argument and return types of crust function in wrap function

[brson]

Thank you! This looks really interesting, but I haven't looked at it closely yet.

I would like some tests, though I realize there's not a way to test this in our current test suite. One thing you could do, that I have done before and would be fine with here, is add some functions to the runtime, possibly under src/rt/rust_test_x86_64.cpp that exhibit some of the problems this is addressing, and prefix them rust_dbg_. Then exercise those functions in some tests.

[brson]

Does this completely fix #1402?

[crabtw]

Yes, it fixes #1402 .
I will add some tests and move ABI dependent code to another module to make it more extensible.

[graydon]

This is fantastic! Thank you so much.

My only concerns are, as you say, modularizing it a bit (per-arch) and making some tests. But I'm happy to do that work myself while integrating it. You did the hard part. Let me know if you prefer to do that yourself or have me do it. It's fine either way.

[crabtw]

I think you can do it better than me, so please do it.
Thank you!

[graydon]

Actually I'm going to land this first and then modularize and test in subsequent steps. Assuming it bootstraps; we do need this sort of code in one form or another.

[graydon]

This is now integrated, thanks! I'm going to leave the issue just a little while longer to remind me to write tests. Modularizing can come later; I just want to make sure it fixes #1402.

[graydon]

Fails testcase I threw together. I'll start debugging. Reopening.

[graydon]

Oh, seems to fail on x86 not x86_64. I think probably that path was broken before, then. I'll file a separate bug on just that case and re-close this. Thanks.