Crash test for issue #3402 of Protobuf PHP extension
Run make and you should get the following crash output:
... copious build log ...
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
string(5) "hello"
[Inferior 1 (process 7) exited normally]