Make sure the compiler knows g_gate_xvlog() and g_gate_xlog() do not

return.  This silences a warning from clang 3.2 about uninitialized use
of the variable 'mediasize' in sbin/ggate/shared/ggate.c.

Reviewed by:	pjd
MFC after:	1 week

shared/ggate.h

@@ -95,8 +95,8 @@ struct g_gate_hdr {
 
 void	g_gate_vlog(int priority, const char *message, va_list ap);
 void	g_gate_log(int priority, const char *message, ...);
-void	g_gate_xvlog(const char *message, va_list ap);
-void	g_gate_xlog(const char *message, ...);
+void	g_gate_xvlog(const char *message, va_list ap) __dead2;
+void	g_gate_xlog(const char *message, ...) __dead2;
 off_t	g_gate_mediasize(int fd);
 unsigned g_gate_sectorsize(int fd);
 void	g_gate_open_device(void);