Consistently use SIGNAL_HANDLER() macro to define signal handler functions

With this change, the signal handler signature is defined in only one place.

Also make most signal handler functions static (those that are only referred to in irc.c).

include/irc_std.h

@@ -160,12 +160,12 @@ typedef int socklen_t;
 
 #include <limits.h>
    
-typedef RETSIGTYPE sigfunc (int);
-sigfunc *my_signal (int, sigfunc *, int);
-
 #define SIGNAL_HANDLER(x) \
 	RETSIGTYPE x (int unused)
 
+typedef SIGNAL_HANDLER(sigfunc);
+sigfunc *my_signal (int, sigfunc *, int);
+
 #include <stdlib.h>
 #define index strchr
 

include/ircterm.h

@@ -709,7 +709,7 @@ extern char default_pair[2];
 #endif
 #endif
 
-	RETSIGTYPE 	term_cont 		(int);
+SIGNAL_HANDLER(term_cont);
 	void 		term_beep 		(void);
 	int		term_echo 		(int);
 	int		term_init 		(char *);

include/screen.h

@@ -40,7 +40,6 @@
 	void	window_redirect (char *, int);
 	void	redraw_resized (Window *, ShrinkInfo, int);
 	void	close_all_screen (void);
-RETSIGTYPE	sig_refresh_screen (int);
 	int	check_screen_redirect (char *);
 	void	BX_kill_screen (Screen *);
 	ShrinkInfo	resize_display (Window *);