* testsuite/lib/libstdc++.exp (check_v3_target_binary_io): New.
	* testsuite/lib/dg-options.exp (dg-require-binary-io): New.
	* testsuite/27_io/basic_filebuf/seekoff/char/1-io.cc,
	testsuite/27_io/basic_filebuf/seekoff/char/2-io.cc,
	testsuite/27_io/basic_filebuf/sgetn/char/1-in.cc,
	testsuite/27_io/basic_filebuf/sgetn/char/1-io.cc,
	testsuite/27_io/basic_filebuf/sgetn/char/2-in.cc,
	testsuite/27_io/basic_filebuf/sgetn/char/2-io.cc,
	testsuite/27_io/basic_filebuf/underflow/wchar_t/11603.cc,
	testsuite/27_io/basic_istream/readsome/char/6746-2.cc,
	testsuite/27_io/basic_istream/readsome/wchar_t/6746-2.cc,
	testsuite/27_io/objects/char/10.cc: Use dg-require-binary-io.

From-SVN: r151825