libstdc++: Use using instead of typedef in opts-common.h

libstdc++-v3/ChangeLog:

	* src/filesystem/ops-common.h (stat_type): Use using.

Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/src/filesystem/ops-common.h

@@ -118,7 +118,7 @@ namespace __gnu_posix
   inline int close(int fd)
   { return ::_close(fd); }
 
-  typedef struct ::__stat64 stat_type;
+  using stat_type = struct ::__stat64;
 
   inline int stat(const wchar_t* path, stat_type* buffer)
   { return ::_wstat64(path, buffer); }
@@ -184,7 +184,7 @@ namespace __gnu_posix
   using ::open;
   using ::close;
 # ifdef _GLIBCXX_HAVE_SYS_STAT_H
-  typedef struct ::stat stat_type;
+  using stat_type = struct ::stat;
   using ::stat;
 #  ifdef _GLIBCXX_USE_LSTAT
   using ::lstat;