Issue Description:

The following commit contains a failing test demonstrating the problem:

martinboehme@f431f1b

It generates a .swiftinterface for module MainModule, but this .swiftinterface then fails to compile with the error message:

MainModule.swiftinterface:6:46: error: cannot find type 'ForeignA' in scope
public func funcTakingForeignStruct(_ param: ForeignA.ForeignStruct)
                                             ^~~~~~~~

To summarize the situation:

• The Swift module SubModule imports Clang modules ForeignA and ForeignB. Both ForeignA and ForeignB include a textual header containing the struct ForeignStruct.

• SubModule re-exports ForeignB but not ForeignA. ForeignStruct is therefore available to clients of SubModule; those clients can use it either using the unqualified name ForeignStruct or the qualified name ForeignB.ForeignStruct, but not ForeignA.ForeignStruct (because SubModule doesn't re-export ForeignA).

• The Swift module MainModule imports SubModule and uses ForeignStruct in the signature of funcTakingForeignStruct. When MainModule is compiled to a .swiftinterface file, that signature erroneously refers to ForeignStruct as ForeignA.ForeignStruct instead of ForeignB.ForeignStruct. Because of this, the resulting .swiftinterface file does not compile.

I discovered this issue in the course of investigating a CI failure on #32404. The repro above corresponds to the situation in the failing test as follows:

• SubModule is Glibc

• ForeignA is SwiftOverlayShims

• ForeignB is SwiftGlibc

• The textual header is sys/time.h, and ForeignStruct is struct timeval

I believe this needs to be fixed in TypePrinter::printModuleContext(), but I'm not sure exactly how.