* cygtls.cc (_cygtls::reset_signal_arrived): New function.

* cygtls.cc (_cygtls::reset_signal_arrived): New function.
(set_signal_arrived::~set_signal_arrived): Use reset_signal_arrived to reset
state.
* exceptions.cc (sig_handle_tty_stop): Use WAIT_SIGNALED rather than assume we
know the return from cancelable_wait.
(_cygtls::interrupt_setup): Modify to allow calling when executing in
non-cygwin code via sigdelayed.  Always reset signal_arrived.
* gendef: Throughout use start_offset rather than the completely wrong
sizeof__cygtls.
(_sigdelayed): Rewrite to avoid duplication when calling the signal handler.
(sigreturn): Delete.
* gentls_offsets: Define start_offset rather than sizeof__cygtls.
* tlsoffsets.h: Regenerate.