* cygthread.cc (cygthread::stub): Accept flag to pass info structure to thread

function.
(cygthread::operator new): Add defense debugging output.
(cygthread::cygthread): Add debugging output.  Set name after thread has been
awakened to avoid a race.
(cygthread::exit_thread): Use handle operator rather than using ev directly.
(cygthread::exit_thread): Reorganize to provide debugging.  Set __name to NULL.
* cygthread.h (cygself): Define.
* fhandler_tty.cc (fhandler_tty_master::init): Use cygself as argument so that
invoked thread can access its own info.
(process_output): Derive cygthread info of thread from thread argument.
* sigproc.cc (sigproc_init): Use cygself as argument so that invoked thread can
access its own info.
(wait_sig): Derive cygthread info of thread from thread argument.

winsup/cygwin/cygthread.h

@@ -29,3 +29,5 @@ class cygthread
   void * operator new (size_t);
   void exit_thread ();
 };
+
+#define cygself NULL