Pending clear answer from WG21 on whether core issue 903 is intended to apply to
C++11 or just C++17, restrict the set of null pointer constants in C++11 mode
back to those which were considered null in C++98.

llvm-svn: 150510
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index c0fff5e..787e722 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -6435,12 +6435,17 @@
   return true;
 }
 
+bool Expr::isCXX98IntegralConstantExpr(ASTContext &Ctx) const {
+  return CheckICE(this, Ctx).Val == 0;
+}
+
 bool Expr::isCXX11ConstantExpr(ASTContext &Ctx, APValue *Result,
                                SourceLocation *Loc) const {
   // We support this checking in C++98 mode in order to diagnose compatibility
   // issues.
   assert(Ctx.getLangOptions().CPlusPlus);
 
+  // Build evaluation settings.
   Expr::EvalStatus Status;
   llvm::SmallVector<PartialDiagnosticAt, 8> Diags;
   Status.Diag = &Diags;