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Issue Description:

For some odd reason, we don't print requirements that we diagnose as "close enough" to another witness that we can offer a rename fixit. For requirements that nearly-match something in another module (especially one you don't control like Foundation), this means the stub we print is missing requirements and doesn't compile.

Look into the callers (or lack thereof) of swift::printRequirementStub to see why this is happening.

I've attached a small SwiftUI Mac app that tries to define a coordinator with a conformance to an Objective-C protocol that defines two requirements. If you open it up and try to build it, only one of the two requirement stubs is printed. The other notes that something in NSObject should be renamed. That remaining stub should be suggested and printed along with the other requirement.