Always zero all elements of siginfo_t throughout.

* cygtls.h (_cygtls::thread_context): Declare new field.
(_cygtls::thread_id): Ditto.
(_cygtls::signal_exit): Move into this class.
(_cygtls::copy_context): Declare new function.
(_cygtls::signal_debugger): Ditto.
* cygtls.cc (_cygtls::init_thread): Fill out thread id field.
* exceptions.cc (exception): Change message when exception info is unknown.
Copy context to thread local storage.
(_cygtls::handle_exceptions): Avoid double test for fault_guarded.  Reflect
move of signal_exit to _cygtls class.
(sigpacket::process): Copy context to thread local storage.
(_cygtls::signal_exit): Move to _cygtls class.  Call signal_debugger to notify
debugger of exiting signal (WIP).  Call stackdump here (WIP).
(_cygtls::copy_context): Define new function.
(_cygtls::signal_debugger): Ditto.
* tlsoffsets.h: Regenerate.
* include/cygwin.h (_fpstate): New internal structure.
(ucontext): Declare new structure (WIP).
(__COPY_CONTEXT_SIZE): New define.
* exceptions.cc (_cygtls::interrupt_setup): Clear "threadkill" field when there
is no sigwaiting thread.
(setup_handler): Move event handling into interrupt_setup.

winsup/cygwin/cygtls.cc

@@ -100,6 +100,7 @@ _cygtls::init_thread (void *x, DWORD (*func) (void *, void *))
       init_exception_handler (handle_exceptions);
     }
 
+  thread_id = GetCurrentThreadId ();
   initialized = CYGTLS_INITIALIZED;
   locals.exitsock = INVALID_SOCKET;
   errno_addr = &(local_clib._errno);