procgen tests could stress outputs harder?

[Gankra]

Right now in procgen we only end up emitting a couple tests that shove the type of interest in the output, or, literally anything in the output.

abi-cafe/src/procgen.rs

Lines 29 to 32 in dd37470

	if !has_refs {
	add_func(out, "val_out", &[], &[ty])?;
	add_func(out, "val_in_out", &[ty], &[ty])?;
	}

There's only so much you can do with Rust and C being our primary languages, given multiple returns don't exist and outparams aren't really outputs abi-wise (and i've consequently refused to reimplement their tedium).

We could generate two copies of each function (one with output, one without). We could generate a struct containing multiple values to return. There's options here, but idk how hard we want to push on it, or which abi exhaustion conditions we're pushing on.