* child_info.h (child_info_fork::parent_wr_proc_pipe): New element.

* fork.cc (fork_parent): Set parent_wr_proc.
* pinfo.cc (set_myself): Close child_proc_info->parent_wr_proc if it exists
rather than trying to get value from parent _pinfo.
* pinfo.h (enum parent_aleter): New enum.
(pinfo::alert_parent): Declare as returning a value.
(pinfo::parent_alive): New function.
* pinfo.cc (pinfo::alert_parent): Set wr_proc_pipe to invalid non-NULL value
when parent disappears.  Return success of operation.
(proc_waiter): Use __ALERT_* enum for control since these are not really
signals.  Implement __ALERT_ALIVE.
* sigproc.cc (my_parent_is_alive): Eliminate.
* sigproc.h (my_parent_is_alive): Ditto for declaration.
(__SIGREPARENT): Eliminate.

winsup/cygwin/fork.cc

@@ -401,6 +401,8 @@ fork_parent (HANDLE& hParent, dll *&first_dll,
   init_child_info (PROC_FORK, &ch, subproc_ready);
 
   ch.forker_finished = forker_finished;
+  ch.parent_wr_proc_pipe = myself->wr_proc_pipe == INVALID_HANDLE_VALUE
+    			   ? NULL : myself->wr_proc_pipe;
 
   stack_base (ch);