Appease -Wnon-virtual-dtor

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169648 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Format/UnwrappedLineParser.h b/lib/Format/UnwrappedLineParser.h
index 92a51ab..908391d 100644
--- a/lib/Format/UnwrappedLineParser.h
+++ b/lib/Format/UnwrappedLineParser.h
@@ -79,6 +79,8 @@
 
 class FormatTokenSource {
 public:
+  virtual ~FormatTokenSource() {
+  }
   virtual FormatToken getNextToken() = 0;
 };