Add NullStmt::Clone and use it

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@71823 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Stmt.cpp b/lib/AST/Stmt.cpp
index 02f5eee..f8f6e06 100644
--- a/lib/AST/Stmt.cpp
+++ b/lib/AST/Stmt.cpp
@@ -98,6 +98,10 @@
   return StatSwitch;
 }
 
+NullStmt* NullStmt::Clone(ASTContext &C) const {
+  return new (C) NullStmt(SemiLoc);
+}
+
 void CompoundStmt::setStmts(ASTContext &C, Stmt **Stmts, unsigned NumStmts) {
   if (this->Body)
     C.Deallocate(Body);