Add missing destructors found with -Wnon-virtual-dtor.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169303 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Format/Format.cpp b/lib/Format/Format.cpp
index 87deccbb..d928aa9 100644
--- a/lib/Format/Format.cpp
+++ b/lib/Format/Format.cpp
@@ -686,6 +686,9 @@
         StructuralError(false) {
   }
 
+  virtual ~Formatter() {
+  }
+
   tooling::Replacements format() {
     UnwrappedLineParser Parser(Lex, SourceMgr, *this);
     StructuralError = Parser.parse();