As Aaron Lehmann just pointed out, I forgot a line...
diff --git a/init/init.c b/init/init.c
index 1a5056c..bca4dd7 100644
--- a/init/init.c
+++ b/init/init.c
@@ -635,6 +635,7 @@
 #ifndef DEBUG_INIT
 static void shutdown_system(void)
 {
+	sigset_t block_signals;
 
 	/* first disable all our signals */
 	sigemptyset(&block_signals);