tests: depcomp: ensure make_ok() fails when run_make fails While running automake tests with -std-gnu=c99, the compiler report errors which lead to make to fail. Yet, these failures are ignored during the tests, which considers them to be successful as stderror is check for one specific pattern. If make fails, investigation should be made to discover why, whatever the reason for the failure is. * t/ax/depcomp.sh: Make make_ok fail when make fails.