Problem: test_shutdown_stress_tipc broken on OSX/Cmake

Solution: include pthread.h in testutil.hpp, removed from
test_shutdown_stress_tipc in an earlier commit

tests/testutil.hpp

@@ -56,6 +56,7 @@
 #       pragma warning(disable:4996)
 #   endif
 #else
+#   include <pthread.h>
 #   include <unistd.h>
 #   include <signal.h>
 #   include <stdlib.h>