Use an alternate signal stack for the unexpected signals on the host.

This lets us report native stack overflow somewhat sensibly.

Change-Id: I841c285b2481aecc6edb0800f385ccc5665067ff
diff --git a/src/runtime_linux.cc b/src/runtime_linux.cc
index 4214003..c96b1e5 100644
--- a/src/runtime_linux.cc
+++ b/src/runtime_linux.cc
@@ -209,7 +209,7 @@
   memset(&action, 0, sizeof(action));
   sigemptyset(&action.sa_mask);
   action.sa_sigaction = HandleUnexpectedSignal;
-  action.sa_flags = SA_RESTART | SA_SIGINFO;
+  action.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
 
   int rc = 0;
   rc += sigaction(SIGILL, &action, NULL);