libbb: introduce bb_signals and bb_signals_recursive,

which sets same handler for many signals. sig_catch is nuked
(bb_signals_recursive is more descriptive name).
*: use them as appropriate. 

function                                             old     new   delta
bb_signals_recursive                                   -      95     +95
bb_signals                                             -      52     +52
run_command                                          258     273     +15
svlogd_main                                         1368    1377      +9
runsv_main                                          1746    1752      +6
runsvdir_main                                       1643    1646      +3
UNSPEC_print                                          64      66      +2
time_main                                           1128    1127      -1
...
resize_main                                          246     210     -36
sig_catch                                             63       -     -63
set_fatal_sighandler                                  85      14     -71
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 5/24 up/down: 182/-548)        Total: -366 bytes

networking/dnsd.c

@@ -361,14 +361,16 @@ int dnsd_main(int argc, char **argv)
 	dnsentryinit();
 
 	signal(SIGINT, interrupt);
-	/* why? signal(SIGPIPE, SIG_IGN); */
-	signal(SIGHUP, SIG_IGN);
+	bb_signals(0
+		/* why? + (1 << SIGPIPE) */
+		+ (1 << SIGHUP)
 #ifdef SIGTSTP
-	signal(SIGTSTP, SIG_IGN);
+		+ (1 << SIGTSTP)
 #endif
 #ifdef SIGURG
-	signal(SIGURG, SIG_IGN);
+		+ (1 << SIGURG)
 #endif
+		, SIG_IGN);
 
 	lsa = xdotted2sockaddr(listen_interface, port);
 	udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);