If we have a custom attribute on a type that does a qualified lookup
into the same type, we need to be able to expand member attribute
macros for that type. As such, the check to see if we already have
a nominal for the attribute would hit a cycle. Limit this check such
that it only applies to local vars, which is the only case where it
actually matters.
rdar://163961797
f2b0b92dc1