Dependencies Scanner: report compiled Swift module paths if they are available

For the explicit module mode, swift-driver uses -compile-module-from-interface to
generate modules from interfaces found by the dependency scanner. However, we don't
need to build the binary module if up-to-date modules are available, either adjacent
to the interface file or in the prebuilt module cache directory. This patch teaches
dependencies scanner to report these ready-to-use binary modules.

lib/Serialization/SerializedModuleLoader.cpp

@@ -366,13 +366,14 @@ llvm::ErrorOr<ModuleDependencies> SerializedModuleLoaderBase::scanModuleFile(
   // Load the module file without validation.
   std::unique_ptr<ModuleFile> loadedModuleFile;
   bool isFramework = false;
+  serialization::ExtendedValidationInfo extInfo;
   serialization::ValidationInfo loadInfo =
       ModuleFile::load(modulePath.str(),
                        std::move(moduleBuf.get()),
                        nullptr,
                        nullptr,
                        isFramework, loadedModuleFile,
-                       nullptr);
+                       &extInfo);
 
   // Map the set of dependencies over to the "module dependencies".
   auto dependencies = ModuleDependencies::forSwiftModule(modulePath.str());