testsuite: Disable tests for C++23 that depend on std::unexpected

These tests depend on unexpected handlers, which are no longer declared
for C++23 mode. Adjust the target specifier so they don't run.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/noexcept06.C: Disable for C++23.

libstdc++-v3/ChangeLog:

	* testsuite/18_support/exception/38732.cc: Disable for C++23.
	* testsuite/18_support/headers/exception/synopsis.cc: Likewise.
	* testsuite/18_support/unexpected_handler.cc: Likewise.

gcc/testsuite/g++.dg/cpp0x/noexcept06.C

@@ -1,6 +1,6 @@
 // Test that checking of a nothrow specification uses the one on the
 // definition.
-// { dg-do run { target c++11 } }
+// { dg-do run { target { c++11 && { ! c++23 } } } }
 // { dg-options "-Wno-terminate" }
 
 #include <exception>

libstdc++-v3/testsuite/18_support/exception/38732.cc

@@ -15,6 +15,8 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+// { dg-do run { target { c++11 && { ! c++23 } } } }
+
 #include <typeinfo>
 #include <exception>
 #include "unwind.h"

libstdc++-v3/testsuite/18_support/headers/exception/synopsis.cc

@@ -1,4 +1,4 @@
-// { dg-do compile { target c++11 } }
+// { dg-do compile { target { c++11 && { ! c++23 } } } }
 
 // Copyright (C) 2007-2022 Free Software Foundation, Inc.
 //

libstdc++-v3/testsuite/18_support/unexpected_handler.cc

@@ -16,7 +16,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-options "-Wno-deprecated-declarations" }
-// { dg-do run { target c++11 } }
+// { dg-do run { target { c++11 && { ! c++23 } } } }
 
 // D.11 Violating exception-specifications