init: actually report which signal is causing the reboot.

It wasn't clear to me why init was rebooting until I saw that it was
SIGABRT, which then made me read through earlier log spam to work out
what was actually unhappy (the SELinux compiler, in my case).

Test: worked out why init was rebooting my device
Change-Id: I605d8956213c4c23711073fd4b0ff99562b7f351
diff --git a/init/util.cpp b/init/util.cpp
index 0532375..40db838 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -20,6 +20,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <pwd.h>
+#include <signal.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -481,7 +482,7 @@
         return;
     }
 
-    InitFatalReboot();
+    InitFatalReboot(SIGABRT);
 }
 
 // The kernel opens /dev/console and uses that fd for stdin/stdout/stderr if there is a serial