Fix memory leak introduced in r237314.

The commit r237314 that implements YAML block parsing
introduced a leak that was caught by the ASAN linux buildbot.
YAML Parser stores its tokens in an ilist, and allocates
tokens using a BumpPtrAllocator, but doesn't call the
destructor for the allocated tokens. R237314 added an 
std::string field to a Token which leaked as the Token's
destructor wasn't called. This commit fixes this leak
by calling the Token's destructor when a Token is being
removed from an ilist of tokens.

llvm-svn: 237389

lib/Support/YAMLParser.cpp

@@ -168,7 +168,7 @@ struct ilist_node_traits<Token> {
   Token *createNode(const Token &V) {
     return new (Alloc.Allocate<Token>()) Token(V);
   }
-  static void deleteNode(Token *V) {}
+  static void deleteNode(Token *V) { V->~Token(); }
 
   void addNodeToList(Token *) {}
   void removeNodeFromList(Token *) {}