* cygthread.cc (cygthread::stub): Detect if thread function wants to release

itself here, to avoid a race.
(cygthread::release): Clear more stuff.  Add a diagnostic for an internal
error.
* cygthread.h (auto_release): New function.
* pinfo.h (pinfo::remember): Add an argument to denote whether child is
detached.
* fork.cc (fork_parent): Reflect change in arguments to pinfo::remember.
* pinfo.cc (_pinfo::exit): Signal exit more forcibly.
(proc_waiter): Use cygthread::auto_release to signify that cygthread::stub
should release the thread.  This should avoid a race.
(pinfo::alert_parent): Don't signify an error when wr_proc_pipe == NULL.
* sigproc.cc (proc_subproc): Add support for PROC_DETACHED_CHILD.
* sigproc.h: Ditto.
* spawn.cc (spawn_guts): Specify whether child is detached or not when calling
pinfo::remember.

winsup/cygwin/pinfo.h

@@ -168,9 +168,10 @@ public:
 #ifndef _SIGPROC_H
   int remember () {system_printf ("remember is not here"); return 0;}
 #else
-  int remember ()
+  int remember (bool detach)
   {
-    int res = proc_subproc (PROC_ADDCHILD, (DWORD) this);
+    int res = proc_subproc (detach ? PROC_DETACHED_CHILD : PROC_ADDCHILD,
+			    (DWORD) this);
     destroy = res ? false : true;
     return res;
   }