[interop][SwiftToCxx] do not emit domain ObjC error values in C++ mode

Author: hyp

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -561,7 +561,8 @@ class ModuleWriter {
 
     SmallVector<ProtocolConformance *, 1> conformances;
     auto errorTypeProto = ctx.getProtocol(KnownProtocolKind::Error);
-    if (ED->lookupConformance(errorTypeProto, conformances)) {
+    if (outputLangMode != OutputLanguageMode::Cxx
+        && ED->lookupConformance(errorTypeProto, conformances)) {
       bool hasDomainCase = std::any_of(ED->getAllElements().begin(),
                                        ED->getAllElements().end(),
                                        [](const EnumElementDecl *elem) {

test/Interop/SwiftToCxx/functions/swift-functions-errors.swift

@@ -13,8 +13,6 @@
 
 // CHECK: }
 
-// XFAIL: *
-
 @_expose(Cxx)
 public enum NaiveErrors : Error {
     case returnError