Add two new AST nodes to represent initialization of an array in terms of
initialization of each array element:

 * ArrayInitLoopExpr is a prvalue of array type with two subexpressions:
   a common expression (an OpaqueValueExpr) that represents the up-front
   computation of the source of the initialization, and a subexpression
   representing a per-element initializer
 * ArrayInitIndexExpr is a prvalue of type size_t representing the current
   position in the loop

This will be used to replace the creation of explicit index variables in lambda
capture of arrays and copy/move construction of classes with array elements,
and also C++17 structured bindings of arrays by value (which inexplicably allow
copying an array by value, unlike all of C++'s other array declarations).

No uses of these nodes are introduced by this change, however.

llvm-svn: 289413
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 776a7f9..0307648 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2899,6 +2899,7 @@
   case UnaryExprOrTypeTraitExprClass:
   case AddrLabelExprClass:
   case GNUNullExprClass:
+  case ArrayInitIndexExprClass:
   case NoInitExprClass:
   case CXXBoolLiteralExprClass:
   case CXXNullPtrLiteralExprClass:
@@ -2975,6 +2976,7 @@
   case ExtVectorElementExprClass:
   case DesignatedInitExprClass:
   case DesignatedInitUpdateExprClass:
+  case ArrayInitLoopExprClass:
   case ParenListExprClass:
   case CXXPseudoDestructorExprClass:
   case CXXStdInitializerListExprClass: