[Bug c/83656] missing -Wbuiltin-declaration-mismatch on declaration without prototype

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83656

--- Comment #4 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #3)
> Patch: https://gcc.gnu.org/ml/gcc-patches/2018-06/msg01645.html

So according to that discussion, it stalled due to producing a bunch of
warnings in autoconf scripts; repeating my comment about autoconf from that
thread: https://gcc.gnu.org/ml/gcc-patches/2018-06/msg01894.html