PR libstdc++/91711 fix failing test

	PR libstdc++/91711
	* testsuite/23_containers/span/get_neg.cc: Avoid ambiguity due to
	0ul being a valid null pointer constant.

From-SVN: r275563

libstdc++-v3/ChangeLog

 2019-09-10  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/91711
+	* testsuite/23_containers/span/get_neg.cc: Avoid ambiguity due to
+	0ul being a valid null pointer constant.
+
 	* include/std/type_traits (__remove_cv_t): New alias template.
 	(is_void, is_integral, is_floating_point, is_pointer)
 	(is_member_object_pointer, is_member_function_pointer, is_null_pointer)

libstdc++-v3/testsuite/23_containers/span/get_neg.cc

@@ -24,7 +24,7 @@
 int
 main()
 {
-  std::span<int, std::dynamic_extent> myspan((int*)nullptr, 0ul);
+  std::span<int, std::dynamic_extent> myspan((int*)nullptr, (std::size_t)0);
   std::get<0>(myspan); // { dg-error "here" }
 }
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }