* exceptions.cc (sig_handle_tty_stop): Avoid races by waiting for both

* exceptions.cc (sig_handle_tty_stop): Avoid races by waiting for both
signal_arrived and for sigCONT.
(sigpacket::process): Enforce sending of both signal_arrived and sigCONT, where
appropriate.
* gendef (sigreturn): Save tls pointer in ebx so that it can jump into
sigdelayed and use the same register.