cwchar (swprintf, vswprintf): Do not use if _GLIBCXX_HAVE_BROKEN_VSWPRINTF.

cwchar (swprintf, vswprintf): Do not use if _GLIBCXX_HAVE_BROKEN_VSWPRINTF.

	* include/c_global/cwchar (swprintf, vswprintf): Do not use if
	_GLIBCXX_HAVE_BROKEN_VSWPRINTF.
	* testsuite/lib/libstdc++.exp (check_v3_target_swprintf): New.
	* testsuite/lib/dg-options.exp (dg-require-swprintf): New.
	* testsuite/21_strings/headers/cwchar/functions_std.cc,
	testsuite/27_io/basic_ostream/inserters_arithmetic/wchar_t/4402.cc,
	testsuite/27_io/basic_ostream/inserters_other/wchar_t/error_code.cc:
	Use dg-require-swprintf.

From-SVN: r150063