When analyzing a struct's layout to determine whether it contains a
single non-empty field, bail upon encountering a field that is not ABI
accessible.
Previously, rather than bailing (though that was the intent), the field
was ignored. The result was that struct's with a single non-empty field
and any number of ABI inaccessible fields would be treated as if they
only had a single non-empty field. Trouble ensued.
rdar://79513293
