Implement -Wunused-label.

llvm-svn: 114315
diff --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index 7a5b949..edd8002 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -213,6 +213,7 @@
   Writer.AddIdentifierRef(S->getID(), Record);
   Writer.AddStmt(S->getSubStmt());
   Writer.AddSourceLocation(S->getIdentLoc(), Record);
+  Record.push_back(S->isUsed());
   Record.push_back(Writer.GetLabelID(S));
   Code = serialization::STMT_LABEL;
 }