[NFC] Add a tablegen node for the root of the AST node hierarchies.

This is useful for the property databases we want to add for abstract
serialization, since root classes can have interesting properties.
diff --git a/clang/utils/TableGen/TableGen.cpp b/clang/utils/TableGen/TableGen.cpp
index 29c6d76..c988a58 100644
--- a/clang/utils/TableGen/TableGen.cpp
+++ b/clang/utils/TableGen/TableGen.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "TableGenBackends.h" // Declares all backends.
+#include "ClangASTEmitters.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Signals.h"
@@ -263,14 +264,14 @@
     EmitClangDiagsIndexName(Records, OS);
     break;
   case GenClangCommentNodes:
-    EmitClangASTNodes(Records, OS, "Comment", "");
+    EmitClangASTNodes(Records, OS, CommentNodeClassName, "");
     break;
   case GenClangDeclNodes:
-    EmitClangASTNodes(Records, OS, "Decl", "Decl");
+    EmitClangASTNodes(Records, OS, DeclNodeClassName, "Decl");
     EmitClangDeclContext(Records, OS);
     break;
   case GenClangStmtNodes:
-    EmitClangASTNodes(Records, OS, "Stmt", "");
+    EmitClangASTNodes(Records, OS, StmtNodeClassName, "");
     break;
   case GenClangTypeNodes:
     EmitClangTypeNodes(Records, OS);