libstdc++: Change compile-only test to run

The 24_iterators/ostream_iterator/1.cc test uses VERIFY and so is
obviously meant to have been run, not just compiled.

	* testsuite/23_containers/unordered_set/allocator/ext_ptr.cc: Add
	comment explaining multiple dg-do directives.
	* testsuite/24_iterators/ostream_iterator/1.cc: Fix do-do directive
	so test is run as well as compiled.

libstdc++-v3/ChangeLog

+2020-03-10  Jonathan Wakely  <jwakely@redhat.com>
+
+	* testsuite/23_containers/unordered_set/allocator/ext_ptr.cc: Add
+	comment explaining multiple dg-do directives.
+	* testsuite/24_iterators/ostream_iterator/1.cc: Fix do-do directive
+	so test is run as well as compiled.
+
 2020-03-09  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/94063

libstdc++-v3/testsuite/23_containers/unordered_set/allocator/ext_ptr.cc

@@ -15,6 +15,8 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+// This test fails to compile since C++17 (see xfail-if below) so we can only
+// do a "run" test for C++11 and C++14, and a "compile" test for C++17 and up.
 // { dg-do run { target { c++11_only || c++14_only } } }
 // { dg-do compile { target c++17 } }
 

libstdc++-v3/testsuite/24_iterators/ostream_iterator/1.cc

@@ -15,7 +15,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-do compile { target c++11 } }
+// { dg-do run { target c++11 } }
 
 #include <iterator>
 #include <sstream>