[Bug c/70958] Flag -Wreturn-type does not warn about lacking return statement in main

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70958

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-std=gnu90 or -std=gnu89 (depending on the naming you like :) ).