swift

8436d4e4 - Set the InMemoryOutputFileSystem on the subinstance that builds referenced .swiftinterface files.

Set the InMemoryOutputFileSystem on the subinstance that builds referenced .swiftinterface files. When the main compiler instance is using an InMemoryOutputFileSystem for its ClangLoader, this should be used by the subinstance loader as well as any files it otherwise writes to the filesystem may not be visible.