Add Sema::isNullPointerConstant which extwarns if necessary. Use it in Sema::CheckConditionalOperands.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@60319 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/Sema.h b/lib/Sema/Sema.h
index 7b69de5..17af72a 100644
--- a/lib/Sema/Sema.h
+++ b/lib/Sema/Sema.h
@@ -1350,7 +1350,9 @@
   /// VerifyIntegerConstantExpression - verifies that an expression is an ICE,
   /// and reports the appropriate diagnostics. Returns false on success.
   /// Can optionally return the value of the expression.
-  bool VerifyIntegerConstantExpression(const Expr* E, llvm::APSInt *Result = 0);
+  bool VerifyIntegerConstantExpression(const Expr*E, llvm::APSInt *Result = 0);
+
+  bool isNullPointerConstant(const Expr *E);
 
   //===--------------------------------------------------------------------===//
   // Extra semantic analysis beyond the C type system