[cxx-interop] Import OS_OBJECT_DECL consistently with and without C++ interop enabled

Previously ClangImporter was not able to lookup `NSObject` when C++ interop is enabled, which caused types such as `xpc_object_t` from system module XPC to be imported differently: `any OS_xpc_object` without C++ interop vs `any NSObject & OS_xpc_object` with C++ interop enabled.

rdar://110000787
(cherry picked from commit 5a62032)

Author: egorzhdan

lib/ClangImporter/ImportType.cpp

@@ -3418,7 +3418,7 @@ static Type getNamedProtocolType(ClangImporter::Implementation &impl,
   clang::LookupResult lookupResult(sema, clangName, clang::SourceLocation(),
                                    clang::Sema::LookupObjCProtocolName);
   lookupResult.setAllowHidden(true);
-  if (!sema.LookupName(lookupResult, /*Scope=*/nullptr))
+  if (!sema.LookupName(lookupResult, /*Scope=*/sema.TUScope))
     return Type();
 
   for (auto decl : lookupResult) {

test/Interop/Cxx/objc-correctness/Inputs/module.modulemap

@@ -18,3 +18,9 @@ module NSNofiticationBridging {
   requires objc
   requires cplusplus
 }
+
+module OSObject {
+  header "os-object.h"
+  requires objc
+  requires cplusplus
+}

test/Interop/Cxx/objc-correctness/Inputs/os-object.h

@@ -0,0 +1,4 @@
+#include <os/object.h>
+
+/// Similar to xpc_object_t
+OS_OBJECT_DECL(my_object);

test/Interop/Cxx/objc-correctness/os-object.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-frontend -typecheck -verify -I %S/Inputs -cxx-interoperability-mode=swift-5.9 %s
+// REQUIRES: objc_interop
+
+import OSObject
+
+extension my_object_t {
+  func dummy() {}
+}