[Bug fortran/57160] short-circuit IF only with -ffrontend-optimize

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57160

--- Comment #12 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> Patch posted at: https://gcc.gnu.org/ml/fortran/2018-07/msg00086.html

Don't abuse any optimization option.