fix -fno-common build

Index: include/irc.h
--- include/irc.h.orig
+++ include/irc.h
@@ -166,6 +166,6 @@ const	char *	current_loader		(void);	 /* XXX command.c
 	char *	current_package		(void);  /* XXX command.c */
 
 /* keep track of signals for scripted events */
-volatile int     signals_caught[NSIG];
+extern volatile int     signals_caught[NSIG];
 
 #endif /* __irc_h */