DiagnosticEngine: Print the ID of the wrapped, not wrapper, diagnostic

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -1086,7 +1086,7 @@ public:
         // Emit a specific unavailable message when we know why a decl can't be
         // exposed, or a generic message otherwise.
         auto diagString =
-            M.getASTContext().Diags.diagnosticStringFor(diag.getID());
+            M.getASTContext().Diags.getFormatStringForDiagnostic(diag.getID());
         DiagnosticEngine::formatDiagnosticText(os, diagString, diag.getArgs(),
                                                DiagnosticFormatOptions());
         os << "\");\n";