Define cxx11-abi effective target for libstdc++ tests

Define cxx11-abi effective target for libstdc++ tests

	PR libstdc++/79075
	* testsuite/lib/libstdc++.exp (check_v3_target_filesystem_ts): Remove
	redundant option from cxxflags.
	(check_effective_target_cxx11-abi): Define.
	* testsuite/21_strings/basic_string/allocator/71964.cc: Use cxx11-abi
	effective target.
	* testsuite/21_strings/basic_string/allocator/char/copy.cc: Likewise.
	* testsuite/21_strings/basic_string/allocator/char/copy_assign.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/char/minimal.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/char/move.cc: Likewise.
	* testsuite/21_strings/basic_string/allocator/char/move_assign.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/char/noexcept.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/char/swap.cc: Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/copy.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/move.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/noexcept.cc:
	Likewise.
	* testsuite/21_strings/basic_string/allocator/wchar_t/swap.cc:
	Likewise.
	* testsuite/23_containers/list/61347.cc: Likewise.
	* testsuite/27_io/basic_fstream/cons/base.cc: Likewise.
	* testsuite/27_io/ios_base/failure/cxx11.cc: Likewise.

From-SVN: r244440