[AST] Store the expressions in ParenListExpr in a trailing array

Use the newly available space in the bit-fields of Stmt
and store the expressions in a trailing array. This saves
2 pointer per ParenListExpr.

Differential Revision: https://reviews.llvm.org/D54675

Reviewed By: rjmccall

llvm-svn: 347320
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index a880818..31607dc 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -6409,8 +6409,8 @@
   if (!ToRParenLocOrErr)
     return ToRParenLocOrErr.takeError();
 
-  return new (Importer.getToContext()) ParenListExpr(
-      Importer.getToContext(), *ToLParenLocOrErr, ToExprs, *ToRParenLocOrErr);
+  return ParenListExpr::Create(Importer.getToContext(), *ToLParenLocOrErr,
+                               ToExprs, *ToRParenLocOrErr);
 }
 
 ExpectedStmt ASTNodeImporter::VisitStmtExpr(StmtExpr *E) {