Cannot look up associated type for imported conformance

Compiler issue on non-Darwin platform(Linux and WASM).

```
Cannot look up associated type for imported conformance:
(struct_type decl=_OpenGraph.(file).OGAttribute)
(associated_type_decl "_ObjectiveCType" access=public overridden=)
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.
Stack dump:
```