* autoload.cc (FindFirstVolumeA): Add.

(FindNextVolumeA): Add.
	(FindVolumeClose): Add.
	(GetVolumePathNamesForVolumeNameA): Add.
	* fhandler.h (class fhandler_base): Declare new method fsync.
	* fhandler.cc (fhandler_base::fsync): New method.
	* syscalls.cc (fsync): Move functionality into fhandler method fsync.
	Just call this method from here.
	(sync_worker): New static function.
	(sync): Fill with life for NT systems.
	* wincap.h (wincaps::has_guid_volumes): New element.
	* wincap.cc: Implement above element throughout.

winsup/cygwin/fhandler.cc

@@ -1623,3 +1623,14 @@ fhandler_base::utimes (const struct timeval *tvp)
   set_errno (EINVAL);
   return -1;
 }
+
+int
+fhandler_base::fsync ()
+{
+  if (pc.isdir ()) /* Just succeed. */
+    return 0;
+  if (FlushFileBuffers (get_handle ()))
+    return 0;
+  __seterrno ();
+  return -1;
+}