leaking_addresses: add SigIgn to false positives

Signal masks are false positives, we already check for SigBlk and SigCgt
but we missed SigIgn.

Add SigIgn to false positive check.
Signed-off-by: Tobin C. Harding <me@tobin.cc>

scripts/leaking_addresses.pl

@@ -228,6 +228,7 @@ sub may_leak_address
 
 	# Signal masks.
 	if ($line =~ '^SigBlk:' or
+	    $line =~ '^SigIgn:' or
 	    $line =~ '^SigCgt:') {
 		return 0;
 	}