added unload feature for cling

Author: kr-2003

lib/Interpreter/CppInterOp.cpp

@@ -3618,7 +3618,10 @@ namespace Cpp {
 
   int Undo(unsigned N) {
 #ifdef CPPINTEROP_USE_CLING
-    return compat::Interpreter::kFailure;
+    auto &I = getInterp();
+    cling::Interpreter::PushTransactionRAII RAII(&I);
+    I.unload(N);
+    return compat::Interpreter::kSuccess;
 #else
     return getInterp().undo(N);
 #endif

unittests/CppInterOp/FunctionReflectionTest.cpp

@@ -1263,11 +1263,7 @@ TEST(FunctionReflectionTest, UndoTest) {
   testing::internal::CaptureStderr();
   Cpp::Process("int y = x;");
   cerrs = testing::internal::GetCapturedStderr();
-  EXPECT_STREQ(
-      cerrs.c_str(),
-      "In file included from <<< inputs >>>:1:\ninput_line_2:1:9: error: use "
-      "of undeclared identifier 'x'\n    1 | int y = x;\n      |         "
-      "^\nFailed to parse via ::process:Parsing failed.\n");
+  EXPECT_TRUE(strstr(cerrs.c_str(), "error: use of undeclared identifier 'x'") != nullptr);
   testing::internal::CaptureStderr();
   Cpp::Process("int x = 10;");
   cerrs = testing::internal::GetCapturedStderr();