Fix clang warning "has virtual functions but non-virtual destructor".

src/IceAssembler.h

 //===- subzero/src/IceAssembler.h - Integrated assembler --------*- C++ -*-===//
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Modified by the Subzero authors.
 //
 //===----------------------------------------------------------------------===//
 //
 //                        The Subzero Code Generator
@@ skipping 28 matching lines @@
 /// A Label can be in one of three states:
 ///  - Unused.
 ///  - Linked, unplaced and tracking the position of branches to the label.
 ///  - Bound, placed and tracking its position.
 class Label {
   Label(const Label &) = delete;
   Label &operator=(const Label &) = delete;
 
 public:
   Label() = default;
-  ~Label() = default;
+  virtual ~Label() = default;
 
   virtual void finalCheck() const {
     // Assert if label is being destroyed with unresolved branches pending.
     assert(!isLinked());
   }
 
   /// Returns the encoded position stored in the label.
   intptr_t getEncodedPosition() const { return Position; }
 
   /// Returns the position for bound labels (branches that come after this are
@@ skipping 301 matching lines @@
 protected:
   // Buffer's constructor uses the Allocator, so it needs to appear after it.
   // TODO(jpp): dependencies on construction order are a nice way of shooting
   // yourself in the foot. Fix this.
   AssemblerBuffer Buffer;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEASSEMBLER_H_