fortify_test.cpp: _FORTIFY_SOURCE=3 should be a superset of 2.

Change-Id: I792d1fef0a58db9738578d58afdea41f5c4a9be6
diff --git a/tests/fortify_test.cpp b/tests/fortify_test.cpp
index ee71f03..fd1680b 100644
--- a/tests/fortify_test.cpp
+++ b/tests/fortify_test.cpp
@@ -43,7 +43,7 @@
 
 using DEATHTEST = SilentDeathTest;
 
-#if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE == 2
+#if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE >= 2
 struct foo {
   char empty[0];
   char one[1];