[interop][SwiftToCxx] forward declare - do not use bridged types in C++ mode

This allows SDK's stdlib Array to correctly decl String forward declaration

Author: hyp

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -366,7 +366,8 @@ class ModuleWriter {
           return;
 
         // Bridge, if necessary.
-        TD = printer.getObjCTypeDecl(TD);
+        if (outputLangMode != OutputLanguageMode::Cxx)
+          TD = printer.getObjCTypeDecl(TD);
 
         if (finder.needsDefinition() && isa<NominalTypeDecl>(TD)) {
           // We can delay individual members of classes; do so if necessary.