[libc++] Modernizes the forwarded ios headers.

libcxx/include/__fwd/fstream.h

 class _LIBCPP_TEMPLATE_VIS basic_filebuf;
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_ifstream;
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_ofstream;
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_fstream;
 
-typedef basic_filebuf<char> filebuf;
-typedef basic_ifstream<char> ifstream;
-typedef basic_ofstream<char> ofstream;
-typedef basic_fstream<char> fstream;
+using filebuf  = basic_filebuf<char>;
+using ifstream = basic_ifstream<char>;
+using ofstream = basic_ofstream<char>;
+using fstream  = basic_fstream<char>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_filebuf<wchar_t> wfilebuf;
-typedef basic_ifstream<wchar_t> wifstream;
-typedef basic_ofstream<wchar_t> wofstream;
-typedef basic_fstream<wchar_t> wfstream;
+using wfilebuf  = basic_filebuf<wchar_t>;
+using wifstream = basic_ifstream<wchar_t>;
+using wofstream = basic_ofstream<wchar_t>;
+using wfstream  = basic_fstream<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(filebuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfilebuf)) basic_filebuf;
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(ifstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wifstream)) basic_ifstream;
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(ofstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wofstream)) basic_ofstream;
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(fstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfstream)) basic_fstream;
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_FSTREAM_H

libcxx/include/__fwd/ios.h

 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_ios;
 
-typedef basic_ios<char> ios;
+using ios = basic_ios<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_ios<wchar_t> wios;
+using wios = basic_ios<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(ios) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wios)) basic_ios;
 
 #if defined(_NEWLIB_VERSION)
 // On newlib, off_t is 'long int'
-typedef long int streamoff; // for char_traits in <string>
+using streamoff = long int; // for char_traits in <string>
 #else
-typedef long long streamoff; // for char_traits in <string>
+using streamoff = long long; // for char_traits in <string>
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_IOS_H

libcxx/include/__fwd/istream.h

 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_istream;
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_iostream;
 
-typedef basic_istream<char> istream;
-typedef basic_iostream<char> iostream;
+using istream  = basic_istream<char>;
+using iostream = basic_iostream<char>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_istream<wchar_t> wistream;
-typedef basic_iostream<wchar_t> wiostream;
+using wistream  = basic_istream<wchar_t>;
+using wiostream = basic_iostream<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(istream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistream)) basic_istream;
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(iostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wiostream)) basic_iostream;
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_ISTREAM_H

libcxx/include/__fwd/ostream.h

 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_ostream;
 
-typedef basic_ostream<char> ostream;
+using ostream = basic_ostream<char>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_ostream<wchar_t> wostream;
+using wostream = basic_ostream<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(ostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostream)) basic_ostream;
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_OSTREAM_H

libcxx/include/__fwd/sstream.h

 
 template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_istringstream;
 template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_ostringstream;
 template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_stringstream;
 
-typedef basic_stringbuf<char> stringbuf;
-typedef basic_istringstream<char> istringstream;
-typedef basic_ostringstream<char> ostringstream;
-typedef basic_stringstream<char> stringstream;
+using stringbuf     = basic_stringbuf<char>;
+using istringstream = basic_istringstream<char>;
+using ostringstream = basic_ostringstream<char>;
+using stringstream  = basic_stringstream<char>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_stringbuf<wchar_t> wstringbuf;
-typedef basic_istringstream<wchar_t> wistringstream;
-typedef basic_ostringstream<wchar_t> wostringstream;
-typedef basic_stringstream<wchar_t> wstringstream;
+using wstringbuf     = basic_stringbuf<wchar_t>;
+using wistringstream = basic_istringstream<wchar_t>;
+using wostringstream = basic_ostringstream<wchar_t>;
+using wstringstream  = basic_stringstream<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits, class _Allocator>
 class _LIBCPP_PREFERRED_NAME(stringbuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringbuf)) basic_stringbuf;
 template <class _CharT, class _Traits, class _Allocator>
 class _LIBCPP_PREFERRED_NAME(istringstream)
     _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistringstream)) basic_istringstream;
 template <class _CharT, class _Traits, class _Allocator>

libcxx/include/__fwd/streambuf.h

 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS basic_streambuf;
 
-typedef basic_streambuf<char> streambuf;
+using streambuf = basic_streambuf<char>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_streambuf<wchar_t> wstreambuf;
+using wstreambuf = basic_streambuf<wchar_t>;
 #endif
 
 template <class _CharT, class _Traits>
 class _LIBCPP_PREFERRED_NAME(streambuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstreambuf)) basic_streambuf;
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_STREAMBUF_H