Fix emission of vtables

It is (again) necessary to call DefineUsedVTables() to enable (at
least) the emission of implicitly defined destructors overriding
the virtual destructor in a base class, see the added test.

lib/Interpreter/IncrementalParser.cpp

@@ -642,6 +642,8 @@ namespace cling {
       Transaction* prevConsumerT = m_Consumer->getTransaction();
       m_Consumer->setTransaction(T);
       Transaction* nestedT = beginTransaction(T->getCompilationOpts());
+      // Process used vtables and generate implicit bodies.
+      getCI()->getSema().DefineUsedVTables();
       // Pull all template instantiations in that came from the consumers.
       getCI()->getSema().PerformPendingInstantiations();
 #ifdef _WIN32

test/CodeGeneration/VTableDestructor.C

@@ -0,0 +1,40 @@
+//------------------------------------------------------------------------------
+// CLING - the C++ LLVM-based InterpreterG :)
+//
+// This file is dual-licensed: you can choose to license it under the University
+// of Illinois Open Source License or the GNU Lesser General Public License. See
+// LICENSE.TXT for details.
+//------------------------------------------------------------------------------
+
+// RUN: cat %s | %cling -Xclang -verify 2>&1 | FileCheck %s
+
+// Test that the interpreter properly generates implicitly defined destructors
+// overriding the virtual destructor in the base class.
+
+// expected-no-diagnostics
+
+.rawInput
+extern "C" int printf(const char*,...);
+
+class A {
+public:
+  virtual ~A() {
+    printf("A::~A()\n");
+  }
+};
+
+class B : public A {
+public:
+  B() {
+    printf("B::B()\n");
+  }
+};
+.rawInput
+
+// CHECK-NOT: error
+// CHECK-NOT: Symbols not found
+
+// CHECK: B::B()
+A *b = new B;
+// CHECK: A::~A()
+delete b;