Add a test for #516 to the test suite

[fitzgen]

r? @rossberg

[rossberg]

Thanks! But since the issue it tests actually is the typing of br_on_null, I think it would be more appropriate to add this test to br_on_null.wast.

[fitzgen]

There isn't a br_on_null.wast in the gc directory. Should I create one?

[rossberg]

It's in the main directory. But you'll need to modify the example to avoid the use of GC features (which should be inessential to the issue). E.g. with some use of subtyping that works with just the funcref proposal.

[fitzgen]

@rossberg rewrote it to use (ref null $ty) and funcref instead of structref and anyref and moved the test into br_on_null.wast.

[rossberg]

Thanks!