* dtable.cc (dtable::build_fhandler): Accept an optional path_conv argument.

If available, use this to calculate path name and device number.
* dtable.h (dtable): Reflect above change.
* fhandler.h (fhandler_base): Declare virtual method which accepts path_conv
rather than path string as first argument.
* fhandler.cc (fhandler_base::open): Define above new method.
* syscalls.cc (_open): Set aside a path_conv variable for use in build_fhandler
and subsequent call to open.

winsup/cygwin/dtable.h

@@ -49,7 +49,8 @@ public:
   void fixup_after_fork (HANDLE);
   fhandler_base *build_fhandler (int fd, DWORD dev, const char *name,
 				 int unit = -1);
-  fhandler_base *build_fhandler (int fd, const char *name, HANDLE h);
+  fhandler_base *build_fhandler (int fd, const char *name, HANDLE h = NULL,
+      				 path_conv *pc = NULL);
   inline int not_open (int fd)
   {
     SetResourceLock (LOCK_FD_LIST, READ_LOCK, "not_open");