Adjust test to pass with old std::string

	* testsuite/21_strings/basic_string/lwg2946.cc: Adjust for
	compatibility with old COW std::string.

From-SVN: r251981

libstdc++-v3/ChangeLog

+2017-09-11  Jonathan Wakely  <jwakely@redhat.com>
+
+	* testsuite/21_strings/basic_string/lwg2946.cc: Adjust for
+	compatibility with old COW std::string.
+
 2017-09-09  Gerald Pfeifer  <gerald@pfeifer.com>
 
 	* doc/xml/manual/allocator.xml: Adjust link for Hoard.

libstdc++-v3/testsuite/21_strings/basic_string/lwg2946.cc

@@ -29,7 +29,7 @@ int main()
   s.assign({"abc", 1});
   s.insert(0, {"abc", 1});
   s.replace(0, 1, {"abc", 1});
-  s.replace(s.cbegin(), s.cbegin(), {"abc", 1});
+  s.replace(s.begin(), s.begin(), {"abc", 1});
   s.find({"abc", 1});
   s.rfind({"abc", 1});
   s.find_first_of({"abc", 1});