[c++1z] N4295: fold-expressions.

This is a new form of expression of the form:

  (expr op ... op expr)

where one of the exprs is a parameter pack. It expands into

  (expr1 op (expr2onwards op ... op expr))

(and likewise if the pack is on the right). The non-pack operand can be
omitted; in that case, an empty pack gives a fallback value or an error,
depending on the operator.

llvm-svn: 221573
diff --git a/clang/lib/AST/ExprClassification.cpp b/clang/lib/AST/ExprClassification.cpp
index 4e2e3ea..915ca16 100644
--- a/clang/lib/AST/ExprClassification.cpp
+++ b/clang/lib/AST/ExprClassification.cpp
@@ -182,6 +182,7 @@
   case Expr::AsTypeExprClass:
   case Expr::ObjCIndirectCopyRestoreExprClass:
   case Expr::AtomicExprClass:
+  case Expr::CXXFoldExprClass:
     return Cl::CL_PRValue;
 
     // Next come the complicated cases.