* pinfo.h (_pinfo::set_exit_state): Declare new function.

(pinfo::exit): Move here from _pinfo::exit.
* sigproc.cc (child_info::sync): Use new function to set exitcode and
process_state.
* pinfo.cc (_pinfo::exit): Ditto.
(proc_waiter): Ditto.
(_pinfo::set_exit_state): Define new function.
(_pinfo::dup_proc_pipe): Close handle when there is no parent process around to
care about the exit value.
* dcrt0.cc (dll_crt0_0): Move subproc_ready synchronization later to make sure
that myself is still mapped in parent.
(do_exit): Reflect movement to pinfo::exit.
(__api_fatal): Ditto.
* exceptions.cc (signal_exit): Ditto.
* errno.cc (errmap): Map PROC_NOT_FOUND.
* init.cc (dll_entry): Release myself before exiting.
* sigproc.cc (proc_can_be_signalled): Set errno appropriately.
(sig_send): Ditto.  Also remove ill-advised test for !myself->sendsig since
this is an indication of a process which is still initializating -- it is not
an error.
(child_info::sync): Don't set exitcode here.  Assume that will happen in
proc_waiter, if necessary.
* spawn.cc (spawn_guts): Delay "wait_for_myself" logic until later.  Don't wait
at all if the process has already exited.  Reflect movement to pinfo::exit.

winsup/cygwin/exceptions.cc

@@ -1080,7 +1080,7 @@ signal_exit (int rc)
 {
   EnterCriticalSection (&exit_lock);
   if (exit_already++)
-    myself->exit (rc);
+    myself.exit (rc);
 
   /* We'd like to stop the main thread from executing but when we do that it
      causes random, inexplicable hangs.  So, instead, we set up the priority