since dtors always have external linkage

issue-912 is xfailed. issue-2111 is already fixed, but it's good to
have the test case.

This was a call to span_bug() before. I'm not sure about the other cases,
but the test case shows that the `vk_self` case can certainly arise with
a bad program, so it should be a span_err() thing and not a span_bug() thing.

Closes #2590

A cleaner way to handle suffix inference for unary minus exprs.

This reverts commit 290206b1.

Forgot to add the actual native code, temporarily reverting.

The first benchmark shows about twice the throughput of the old system.