* signals.c: New file.

    * signals.c: New file.
        * Makefile.in: Add signals.o.
        * target.c (struct signals, target_signal_to_name)
        (target_signal_from_name, target_signal_from_host)
        (do_target_signal_to_host, target_signal_to_host_p)
        (target_signal_to_host, target_signal_from_command): Move to
        signals.c.
        (initialize_targets): Move check of struct signals to...
        * signals.c (_initialize_signals): Here.