Define C++11 version of std::ios_base::failure.

	* config/abi/pre/gnu.ver: Add new exports.
	* include/bits/ios_base.h (ios_base::failure): New definition using
	abi_tag.
	(io_errc, make_error_code, make_error_category, iostream_category):
	Define.
	* include/std/system_error (system_error): Add char* constructors.
	* src/c++11/Makefile.am: Add new file.
	* src/c++11/Makefile.in: Regenerate.
	* src/c++11/cxx11-ios_failure.cc: New file.
	* src/c++98/ios_failure.cc: Compile old definition without abi_tag.
	* testsuite/27_io/ios_base/failure/cxx11.cc: New.
	* testsuite/27_io/ios_base/failure/what-1.cc: Allow string returned by
	ios_base::failure::what() to contain additional data.
	* testsuite/27_io/ios_base/failure/what-2.cc: Likewise..
	* testsuite/27_io/ios_base/failure/what-3.cc: Likewise..
	* testsuite/27_io/ios_base/failure/what-big.cc: Likewise..

From-SVN: r217559