[ScanDependency] Allow importing binary testable module when no interface

Follow-up adjustment for binary module selection in dependency scanning
time. If a testable binary module doesn't have an interface file, it
should be used even it might pull in more dependencies.

include/swift/Serialization/SerializedModuleLoader.h

@@ -163,8 +163,10 @@ protected:
   }
 
   /// Scan the given serialized module file to determine dependencies.
-  llvm::ErrorOr<ModuleDependencyInfo>
-  scanModuleFile(Twine modulePath, bool isFramework, bool isTestableImport);
+  llvm::ErrorOr<ModuleDependencyInfo> scanModuleFile(Twine modulePath,
+                                                     bool isFramework,
+                                                     bool isTestableImport,
+                                                     bool hasInterface);
 
   struct BinaryModuleImports {
     llvm::StringSet<> moduleImports;