Function patch_seq_signal_trap 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn patch_seq_signal_trap(stack: Stack) -> Stack

Trap a signal: install handler that sets flag instead of default behavior

Stack effect: ( signal-num – )

After trapping, the signal will set an internal flag instead of its default action (which might be to terminate the process). Use signal.received? to check and clear the flag.

Safety

Stack must have an Int (signal number) on top