[crt][test] Make ctor_dtor.c robust if DT_INIT/DT_FINI is disabled

New ports in glibc typically don't define ELF_INITFINI, so
DT_INIT/DT_FINI support is disabled.
(rhel ppc64le likely patches their glibc this way as well.)
musl can disable DT_INIT/DT_FINI via -DNO_LEGACY_INITFINI.

So we cannot guarantee ctor()/dtor() will be printed.