Add second path_conv * argument to fstat()s throughout.

* fhandler.h: Change read and fstat to regparm/stdcall throughout.
(fhandler_base::fstat): Just declare.  Don't define.
(fhandler_disk_file::fstat_helper): Declare.
* fhandler.cc (fhandler_base::fstat): Move here from fhandler.h, adapt from
former stat_dev().
(fhandler_disk_file::fstat): Move most of the disk-file-specific logic from
stat_worker to here.  Use fstat_helper to derive final fstat output.
(fhandler_disk_file::fstat_helper): New method, renamed from former fstat
method.
(num_entries): Moved here from syscalls.cc.
* fhandler_mem.cc (fhandler_dev_mem::fstat): Use base class to initialize most
stuff.  Invert has_physical_mem_access test for establishing permissions.
* fhandler_raw.cc (fhandler_dev_raw::fstat): Eliminate unneed test and memory
clearing.  Use base class to initialize most stuff.
* syscalls.cc (stat_dev): Eliminate.
(stat_worker): Simply call fstat method to generate fstat output.  Move all
device specific code to appropriate fstats.
* dir.cc (opendir): Pass correct arg to stat_worker to allow following
symlinks.

winsup/cygwin/fhandler_tape.cc

@@ -148,11 +148,11 @@ fhandler_dev_tape::close (void)
 }
 
 int
-fhandler_dev_tape::fstat (struct stat *buf)
+fhandler_dev_tape::fstat (struct stat *buf, path_conv *pc)
 {
   int ret;
 
-  if (! (ret = fhandler_dev_raw::fstat (buf)))
+  if (!(ret = fhandler_dev_raw::fstat (buf, pc)))
     {
       struct mtget get;