[Dependency Scanning][C++ Interop] Remap lookup of Clang module 'CxxStdlib' to 'std'

Otherwise querying this clang module, e.g. from the corresponding Swift overlay's underlying module import, will fail, since no such module exists.

Resolves rdar://151718115

include/swift/AST/ModuleDependencies.h

@@ -164,6 +164,11 @@ struct ScannerImportStatementInfo {
       : importLocations({location}), importIdentifier(importIdentifier),
         isExported(isExported) {}
 
+  ScannerImportStatementInfo(std::string importIdentifier, bool isExported,
+                             SmallVector<ImportDiagnosticLocationInfo, 4> locations)
+      : importLocations(locations), importIdentifier(importIdentifier),
+        isExported(isExported) {}
+
   void addImportLocation(ImportDiagnosticLocationInfo location) {
     importLocations.push_back(location);
   }